diff --git a/python/psi-api/src/com/jetbrains/python/psi/PyStubElementType.java b/python/psi-api/src/com/jetbrains/python/psi/PyStubElementType.java
index 63aa84ac338a..7ac7547e2c47 100644
--- a/python/psi-api/src/com/jetbrains/python/psi/PyStubElementType.java
+++ b/python/psi-api/src/com/jetbrains/python/psi/PyStubElementType.java
@@ -24,9 +24,10 @@ public abstract class PyStubElementType<StubT extends StubElement, PsiT extends
 
   public abstract PsiElement createElement(@NotNull final ASTNode node);
 
-  public void indexStub(final StubT stub, final IndexSink sink) {
+  public void indexStub(@NotNull final StubT stub, @NotNull final IndexSink sink) {
   }
 
+  @NotNull
   public String getExternalId() {
     return "py." + super.toString();
   }
diff --git a/python/src/com/jetbrains/python/documentation/doctest/PyDocstringFileElementType.java b/python/src/com/jetbrains/python/documentation/doctest/PyDocstringFileElementType.java
index 79ba90fb92b2..0b21e9eb8949 100644
--- a/python/src/com/jetbrains/python/documentation/doctest/PyDocstringFileElementType.java
+++ b/python/src/com/jetbrains/python/documentation/doctest/PyDocstringFileElementType.java
@@ -2,6 +2,7 @@ package com.jetbrains.python.documentation.doctest;
 
 import com.intellij.lang.Language;
 import com.jetbrains.python.psi.PyFileElementType;
+import org.jetbrains.annotations.NotNull;
 
 /**
  * User : ktisha
@@ -11,6 +12,7 @@ public class PyDocstringFileElementType extends PyFileElementType {
     super(language);
   }
 
+  @NotNull
   @Override
   public String getExternalId() {
     return "PyDocstring.FILE";
diff --git a/python/src/com/jetbrains/python/psi/PyFileElementType.java b/python/src/com/jetbrains/python/psi/PyFileElementType.java
index a4bb261665f2..355818dede2e 100644
--- a/python/src/com/jetbrains/python/psi/PyFileElementType.java
+++ b/python/src/com/jetbrains/python/psi/PyFileElementType.java
@@ -128,20 +128,22 @@ public class PyFileElementType extends IStubFileElementType<PyFileStub> {
     return ((PyFile)file).getLanguageLevel();
   }
 
+  @NotNull
   @Override
   public String getExternalId() {
     return "python.FILE";
   }
 
   @Override
-  public void serialize(PyFileStub stub, StubOutputStream dataStream) throws IOException {
+  public void serialize(@NotNull PyFileStub stub, @NotNull StubOutputStream dataStream) throws IOException {
     writeNullableList(dataStream, stub.getDunderAll());
     writeBitSet(dataStream, stub.getFutureFeatures());
     dataStream.writeName(stub.getDeprecationMessage());
   }
 
+  @NotNull
   @Override
-  public PyFileStub deserialize(StubInputStream dataStream, StubElement parentStub) throws IOException {
+  public PyFileStub deserialize(@NotNull StubInputStream dataStream, StubElement parentStub) throws IOException {
     List<String> all = readNullableList(dataStream);
     BitSet future_features = readBitSet(dataStream);
     StringRef deprecationMessage = dataStream.readName();
diff --git a/python/src/com/jetbrains/python/psi/impl/stubs/PyAnnotationElementType.java b/python/src/com/jetbrains/python/psi/impl/stubs/PyAnnotationElementType.java
index 7512acd3befd..daa5038f2f45 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PyAnnotationElementType.java
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PyAnnotationElementType.java
@@ -38,11 +38,12 @@ public class PyAnnotationElementType extends PyStubElementType<PyAnnotationStub,
     return new PyAnnotationImpl(node);
   }
 
-  public void serialize(final PyAnnotationStub stub, final StubOutputStream dataStream)
+  public void serialize(@NotNull final PyAnnotationStub stub, @NotNull final StubOutputStream dataStream)
       throws IOException {
   }
 
-  public PyAnnotationStub deserialize(final StubInputStream dataStream, final StubElement parentStub)
+  @NotNull
+  public PyAnnotationStub deserialize(@NotNull final StubInputStream dataStream, final StubElement parentStub)
       throws IOException {
     return new PyAnnotationStubImpl(parentStub, PyElementTypes.ANNOTATION);
   }
diff --git a/python/src/com/jetbrains/python/psi/impl/stubs/PyClassElementType.java b/python/src/com/jetbrains/python/psi/impl/stubs/PyClassElementType.java
index 0f2082aae00c..5b584b2d2822 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PyClassElementType.java
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PyClassElementType.java
@@ -54,7 +54,7 @@ public class PyClassElementType extends PyStubElementType<PyClassStub, PyClass>
                                getStubElementType());
   }
 
-  public void serialize(final PyClassStub pyClassStub, final StubOutputStream dataStream) throws IOException {
+  public void serialize(@NotNull final PyClassStub pyClassStub, @NotNull final StubOutputStream dataStream) throws IOException {
     dataStream.writeName(pyClassStub.getName());
     final PyQualifiedName[] classes = pyClassStub.getSuperClasses();
     dataStream.writeByte(classes.length);
@@ -66,7 +66,8 @@ public class PyClassElementType extends PyStubElementType<PyClassStub, PyClass>
     dataStream.writeUTFFast(docString != null ? docString : "");
   }
 
-  public PyClassStub deserialize(final StubInputStream dataStream, final StubElement parentStub) throws IOException {
+  @NotNull
+  public PyClassStub deserialize(@NotNull final StubInputStream dataStream, final StubElement parentStub) throws IOException {
     String name = StringRef.toString(dataStream.readName());
     int superClassCount = dataStream.readByte();
     PyQualifiedName[] superClasses = new PyQualifiedName[superClassCount];
@@ -78,7 +79,7 @@ public class PyClassElementType extends PyStubElementType<PyClassStub, PyClass>
     return new PyClassStubImpl(name, parentStub, superClasses, slots, docString.length() > 0 ? docString : null, getStubElementType());
   }
 
-  public void indexStub(final PyClassStub stub, final IndexSink sink) {
+  public void indexStub(@NotNull final PyClassStub stub, @NotNull final IndexSink sink) {
     final String name = stub.getName();
     if (name != null) {
       sink.occurrence(PyClassNameIndex.KEY, name);
diff --git a/python/src/com/jetbrains/python/psi/impl/stubs/PyDecoratorCallElementType.java b/python/src/com/jetbrains/python/psi/impl/stubs/PyDecoratorCallElementType.java
index 9eff8fae4d23..1d78a798d5aa 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PyDecoratorCallElementType.java
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PyDecoratorCallElementType.java
@@ -36,11 +36,12 @@ public class PyDecoratorCallElementType extends PyStubElementType<PyDecoratorStu
     return new PyDecoratorStubImpl(psi.getQualifiedName(), parentStub);
   }
 
-  public void serialize(PyDecoratorStub stub, StubOutputStream dataStream) throws IOException {
+  public void serialize(@NotNull PyDecoratorStub stub, @NotNull StubOutputStream dataStream) throws IOException {
     PyQualifiedName.serialize(stub.getQualifiedName(), dataStream);
   }
 
-  public PyDecoratorStub deserialize(StubInputStream dataStream, StubElement parentStub) throws IOException {
+  @NotNull
+  public PyDecoratorStub deserialize(@NotNull StubInputStream dataStream, StubElement parentStub) throws IOException {
     PyQualifiedName q_name = PyQualifiedName.deserialize(dataStream);
     return new PyDecoratorStubImpl(q_name, parentStub);
   }
diff --git a/python/src/com/jetbrains/python/psi/impl/stubs/PyDecoratorListElementType.java b/python/src/com/jetbrains/python/psi/impl/stubs/PyDecoratorListElementType.java
index ea8bcb2ccb1f..20a164eb04eb 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PyDecoratorListElementType.java
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PyDecoratorListElementType.java
@@ -36,11 +36,12 @@ public class PyDecoratorListElementType extends PyStubElementType<PyDecoratorLis
     return new PyDecoratorListStubImpl(parentStub);
   }
 
-  public void serialize(final PyDecoratorListStub stub, final StubOutputStream dataStream) throws IOException {
+  public void serialize(@NotNull final PyDecoratorListStub stub, @NotNull final StubOutputStream dataStream) throws IOException {
     // nothing
   }
 
-  public PyDecoratorListStub deserialize(final StubInputStream dataStream, final StubElement parentStub) throws IOException {
+  @NotNull
+  public PyDecoratorListStub deserialize(@NotNull final StubInputStream dataStream, final StubElement parentStub) throws IOException {
     return new PyDecoratorListStubImpl(parentStub);
   }
 }
diff --git a/python/src/com/jetbrains/python/psi/impl/stubs/PyExceptPartElementType.java b/python/src/com/jetbrains/python/psi/impl/stubs/PyExceptPartElementType.java
index 9561982856e1..b859f42e5cde 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PyExceptPartElementType.java
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PyExceptPartElementType.java
@@ -37,11 +37,12 @@ public class PyExceptPartElementType extends PyStubElementType<PyExceptPartStub,
   }
 
   @Override
-  public void serialize(PyExceptPartStub stub, StubOutputStream dataStream) throws IOException {
+  public void serialize(@NotNull PyExceptPartStub stub, @NotNull StubOutputStream dataStream) throws IOException {
   }
 
+  @NotNull
   @Override
-  public PyExceptPartStub deserialize(StubInputStream dataStream, StubElement parentStub) throws IOException {
+  public PyExceptPartStub deserialize(@NotNull StubInputStream dataStream, StubElement parentStub) throws IOException {
     return new PyExceptPartStubImpl(parentStub);
   }
 }
diff --git a/python/src/com/jetbrains/python/psi/impl/stubs/PyFromImportStatementElementType.java b/python/src/com/jetbrains/python/psi/impl/stubs/PyFromImportStatementElementType.java
index f7102b927576..337d76e998ff 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PyFromImportStatementElementType.java
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PyFromImportStatementElementType.java
@@ -44,14 +44,15 @@ public class PyFromImportStatementElementType extends PyStubElementType<PyFromIm
                                              getStubElementType());
   }
 
-  public void serialize(PyFromImportStatementStub stub, StubOutputStream dataStream) throws IOException {
+  public void serialize(@NotNull PyFromImportStatementStub stub, @NotNull StubOutputStream dataStream) throws IOException {
     final PyQualifiedName qName = stub.getImportSourceQName();
     PyQualifiedName.serialize(qName, dataStream);
     dataStream.writeBoolean(stub.isStarImport());
     dataStream.writeVarInt(stub.getRelativeLevel());
   }
 
-  public PyFromImportStatementStub deserialize(StubInputStream dataStream, StubElement parentStub) throws IOException {
+  @NotNull
+  public PyFromImportStatementStub deserialize(@NotNull StubInputStream dataStream, StubElement parentStub) throws IOException {
     PyQualifiedName qName = PyQualifiedName.deserialize(dataStream);
     boolean isStarImport = dataStream.readBoolean();
     int relativeLevel = dataStream.readVarInt();
diff --git a/python/src/com/jetbrains/python/psi/impl/stubs/PyFunctionElementType.java b/python/src/com/jetbrains/python/psi/impl/stubs/PyFunctionElementType.java
index 097e12e82425..d7b3292b0364 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PyFunctionElementType.java
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PyFunctionElementType.java
@@ -44,21 +44,22 @@ public class PyFunctionElementType extends PyStubElementType<PyFunctionStub, PyF
                                   message == null ? null : StringRef.fromString(message), parentStub, getStubElementType());
   }
 
-  public void serialize(final PyFunctionStub stub, final StubOutputStream dataStream)
+  public void serialize(@NotNull final PyFunctionStub stub, @NotNull final StubOutputStream dataStream)
       throws IOException {
     dataStream.writeName(stub.getName());
     dataStream.writeUTFFast(stub.getDocString() != null ? stub.getDocString() : "");
     dataStream.writeName(stub.getDeprecationMessage());
   }
 
-  public PyFunctionStub deserialize(final StubInputStream dataStream, final StubElement parentStub) throws IOException {
+  @NotNull
+  public PyFunctionStub deserialize(@NotNull final StubInputStream dataStream, final StubElement parentStub) throws IOException {
     String name = StringRef.toString(dataStream.readName());
     String docString = dataStream.readUTFFast();
     StringRef deprecationMessage = dataStream.readName();
     return new PyFunctionStubImpl(name, docString.length() > 0 ? docString : null, deprecationMessage, parentStub, getStubElementType());
   }
 
-  public void indexStub(final PyFunctionStub stub, final IndexSink sink) {
+  public void indexStub(@NotNull final PyFunctionStub stub, @NotNull final IndexSink sink) {
     final String name = stub.getName();
     if (name != null) {
       sink.occurrence(PyFunctionNameIndex.KEY, name);
diff --git a/python/src/com/jetbrains/python/psi/impl/stubs/PyImportElementElementType.java b/python/src/com/jetbrains/python/psi/impl/stubs/PyImportElementElementType.java
index 3cbc48b5fa9b..e2d6dad14c8e 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PyImportElementElementType.java
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PyImportElementElementType.java
@@ -46,12 +46,13 @@ public class PyImportElementElementType extends PyStubElementType<PyImportElemen
     return new PyImportElementStubImpl(psi.getImportedQName(), asName != null ? asName.getName() : "", parentStub, getStubElementType());
   }
 
-  public void serialize(PyImportElementStub stub, StubOutputStream dataStream) throws IOException {
+  public void serialize(@NotNull PyImportElementStub stub, @NotNull StubOutputStream dataStream) throws IOException {
     PyQualifiedName.serialize(stub.getImportedQName(), dataStream);
     dataStream.writeName(stub.getAsName());
   }
 
-  public PyImportElementStub deserialize(StubInputStream dataStream, StubElement parentStub) throws IOException {
+  @NotNull
+  public PyImportElementStub deserialize(@NotNull StubInputStream dataStream, StubElement parentStub) throws IOException {
     PyQualifiedName qName = PyQualifiedName.deserialize(dataStream);
     StringRef asName = dataStream.readName();
     return new PyImportElementStubImpl(qName, asName.getString(), parentStub, getStubElementType());
diff --git a/python/src/com/jetbrains/python/psi/impl/stubs/PyImportStatementElementType.java b/python/src/com/jetbrains/python/psi/impl/stubs/PyImportStatementElementType.java
index ce601bf00e60..df3ea1619039 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PyImportStatementElementType.java
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PyImportStatementElementType.java
@@ -42,10 +42,11 @@ public class PyImportStatementElementType extends PyStubElementType<PyImportStat
     return new PyImportStatementStubImpl(parentStub, getStubElementType());
   }
 
-  public void serialize(PyImportStatementStub stub, StubOutputStream dataStream) throws IOException {
+  public void serialize(@NotNull PyImportStatementStub stub, @NotNull StubOutputStream dataStream) throws IOException {
   }
 
-  public PyImportStatementStub deserialize(StubInputStream dataStream, StubElement parentStub) throws IOException {
+  @NotNull
+  public PyImportStatementStub deserialize(@NotNull StubInputStream dataStream, StubElement parentStub) throws IOException {
     return new PyImportStatementStubImpl(parentStub, getStubElementType());
   }
 
diff --git a/python/src/com/jetbrains/python/psi/impl/stubs/PyNamedParameterElementType.java b/python/src/com/jetbrains/python/psi/impl/stubs/PyNamedParameterElementType.java
index a415b71cdff0..f7da0ca0f77c 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PyNamedParameterElementType.java
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PyNamedParameterElementType.java
@@ -45,7 +45,7 @@ public class PyNamedParameterElementType extends PyStubElementType<PyNamedParame
     return new PyNamedParameterImpl(node);
   }
 
-  public void serialize(final PyNamedParameterStub stub, final StubOutputStream dataStream)
+  public void serialize(@NotNull final PyNamedParameterStub stub, @NotNull final StubOutputStream dataStream)
       throws IOException {
     dataStream.writeName(stub.getName());
 
@@ -56,7 +56,8 @@ public class PyNamedParameterElementType extends PyStubElementType<PyNamedParame
     dataStream.writeByte(flags);
   }
 
-  public PyNamedParameterStub deserialize(final StubInputStream dataStream, final StubElement parentStub) throws IOException {
+  @NotNull
+  public PyNamedParameterStub deserialize(@NotNull final StubInputStream dataStream, final StubElement parentStub) throws IOException {
     String name = StringRef.toString(dataStream.readName());
     byte flags = dataStream.readByte();
     return new PyNamedParameterStubImpl(name,
diff --git a/python/src/com/jetbrains/python/psi/impl/stubs/PyParameterListElementType.java b/python/src/com/jetbrains/python/psi/impl/stubs/PyParameterListElementType.java
index 4ed964b1bf31..117e0d15dd50 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PyParameterListElementType.java
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PyParameterListElementType.java
@@ -39,11 +39,12 @@ public class PyParameterListElementType extends PyStubElementType<PyParameterLis
     return new PyParameterListImpl(node);
   }
 
-  public void serialize(final PyParameterListStub stub, final StubOutputStream dataStream)
+  public void serialize(@NotNull final PyParameterListStub stub, @NotNull final StubOutputStream dataStream)
       throws IOException {
   }
 
-  public PyParameterListStub deserialize(final StubInputStream dataStream, final StubElement parentStub)
+  @NotNull
+  public PyParameterListStub deserialize(@NotNull final StubInputStream dataStream, final StubElement parentStub)
       throws IOException {
     return new PyParameterListStubImpl(parentStub, getStubElementType());
   }
diff --git a/python/src/com/jetbrains/python/psi/impl/stubs/PySingleStarParameterElementType.java b/python/src/com/jetbrains/python/psi/impl/stubs/PySingleStarParameterElementType.java
index f8a6c30d850e..efed4a53a3a4 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PySingleStarParameterElementType.java
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PySingleStarParameterElementType.java
@@ -36,10 +36,11 @@ public class PySingleStarParameterElementType extends PyStubElementType<PySingle
     return new PySingleStarParameterStubImpl(parentStub);
   }
 
-  public void serialize(PySingleStarParameterStub stub, StubOutputStream dataStream) throws IOException {
+  public void serialize(@NotNull PySingleStarParameterStub stub, @NotNull StubOutputStream dataStream) throws IOException {
   }
 
-  public PySingleStarParameterStub deserialize(StubInputStream dataStream, StubElement parentStub) throws IOException {
+  @NotNull
+  public PySingleStarParameterStub deserialize(@NotNull StubInputStream dataStream, StubElement parentStub) throws IOException {
     return new PySingleStarParameterStubImpl(parentStub);
   }
 }
diff --git a/python/src/com/jetbrains/python/psi/impl/stubs/PyTargetExpressionElementType.java b/python/src/com/jetbrains/python/psi/impl/stubs/PyTargetExpressionElementType.java
index 8746316dd50d..d7f2669adeeb 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PyTargetExpressionElementType.java
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PyTargetExpressionElementType.java
@@ -70,7 +70,7 @@ public class PyTargetExpressionElementType extends PyStubElementType<PyTargetExp
     return new PyTargetExpressionStubImpl(name, initializerType, initializer, psi.getQualifier() != null, parentStub);
   }
 
-  public void serialize(final PyTargetExpressionStub stub, final StubOutputStream stream)
+  public void serialize(@NotNull final PyTargetExpressionStub stub, @NotNull final StubOutputStream stream)
       throws IOException {
     stream.writeName(stub.getName());
     stream.writeVarInt(stub.getInitializerType().getIndex());
@@ -85,7 +85,8 @@ public class PyTargetExpressionElementType extends PyStubElementType<PyTargetExp
     }
   }
 
-  public PyTargetExpressionStub deserialize(final StubInputStream stream, final StubElement parentStub)
+  @NotNull
+  public PyTargetExpressionStub deserialize(@NotNull final StubInputStream stream, final StubElement parentStub)
       throws IOException {
     String name = StringRef.toString(stream.readName());
     PyTargetExpressionStub.InitializerType initializerType = PyTargetExpressionStub.InitializerType.fromIndex(stream.readVarInt());
@@ -126,7 +127,7 @@ public class PyTargetExpressionElementType extends PyStubElementType<PyTargetExp
   }
 
   @Override
-  public void indexStub(PyTargetExpressionStub stub, IndexSink sink) {
+  public void indexStub(@NotNull PyTargetExpressionStub stub, @NotNull IndexSink sink) {
     String name = stub.getName();
     if (name != null && PyUtil.getInitialUnderscores(name) == 0) {
       if (stub.getParentStub() instanceof PyFileStub) {
diff --git a/python/src/com/jetbrains/python/psi/impl/stubs/PyTupleParameterElementType.java b/python/src/com/jetbrains/python/psi/impl/stubs/PyTupleParameterElementType.java
index f4a7af1df982..a2d2720657a8 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PyTupleParameterElementType.java
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PyTupleParameterElementType.java
@@ -34,12 +34,13 @@ public class PyTupleParameterElementType extends PyStubElementType<PyTupleParame
     return new PyTupleParameterStubImpl(psi.hasDefaultValue(), parentStub);
   }
 
-  public PyTupleParameterStub deserialize(StubInputStream dataStream, StubElement parentStub) throws IOException {
+  @NotNull
+  public PyTupleParameterStub deserialize(@NotNull StubInputStream dataStream, StubElement parentStub) throws IOException {
     boolean hasDefaultValue = dataStream.readBoolean();
     return new PyTupleParameterStubImpl(hasDefaultValue, parentStub);
   }
 
-  public void serialize(PyTupleParameterStub stub, StubOutputStream dataStream) throws IOException {
+  public void serialize(@NotNull PyTupleParameterStub stub, @NotNull StubOutputStream dataStream) throws IOException {
     dataStream.writeBoolean(stub.hasDefaultValue());
   }
 }