diff --git a/java/java-impl/src/com/intellij/openapi/projectRoots/impl/JavaSdkImpl.java b/java/java-impl/src/com/intellij/openapi/projectRoots/impl/JavaSdkImpl.java
index ad59dda1c471..eb3ea75c8024 100644
--- a/java/java-impl/src/com/intellij/openapi/projectRoots/impl/JavaSdkImpl.java
+++ b/java/java-impl/src/com/intellij/openapi/projectRoots/impl/JavaSdkImpl.java
@@ -109,25 +109,25 @@ public class JavaSdkImpl extends JavaSdk {
   }
 
   @Override
-  public void saveAdditionalData(SdkAdditionalData additionalData, Element additional) {
+  public void saveAdditionalData(@NotNull SdkAdditionalData additionalData, @NotNull Element additional) {
   }
 
   @Override
   @SuppressWarnings({"HardCodedStringLiteral"})
-  public String getBinPath(Sdk sdk) {
+  public String getBinPath(@NotNull Sdk sdk) {
     return getConvertedHomePath(sdk) + "bin";
   }
 
   @Override
   @NonNls
-  public String getToolsPath(Sdk sdk) {
+  public String getToolsPath(@NotNull Sdk sdk) {
     final String versionString = sdk.getVersionString();
     final boolean isJdk1_x = versionString != null && (versionString.contains("1.0") || versionString.contains("1.1"));
     return getConvertedHomePath(sdk) + "lib" + File.separator + (isJdk1_x? "classes.zip" : "tools.jar");
   }
 
   @Override
-  public String getVMExecutablePath(Sdk sdk) {
+  public String getVMExecutablePath(@NotNull Sdk sdk) {
     /*
     if ("64".equals(System.getProperty("sun.arch.data.model"))) {
       return getBinPath(sdk) + File.separator + System.getProperty("os.arch") + File.separator + VM_EXE_NAME;
diff --git a/java/openapi/src/com/intellij/openapi/projectRoots/JavaSdk.java b/java/openapi/src/com/intellij/openapi/projectRoots/JavaSdk.java
index 88a5c55c1c2a..51ae01f5c1b9 100644
--- a/java/openapi/src/com/intellij/openapi/projectRoots/JavaSdk.java
+++ b/java/openapi/src/com/intellij/openapi/projectRoots/JavaSdk.java
@@ -25,7 +25,7 @@ import org.jetbrains.annotations.Nullable;
 import java.io.File;
 
 public abstract class JavaSdk extends SdkType implements JavaSdkType, ApplicationComponent {
-  public JavaSdk(@NonNls String name) {
+  public JavaSdk(@NotNull @NonNls String name) {
     super(name);
   }
 
diff --git a/platform/lang-api/src/com/intellij/openapi/projectRoots/SdkType.java b/platform/lang-api/src/com/intellij/openapi/projectRoots/SdkType.java
index b20f1f75ac8d..e5aa799a775f 100644
--- a/platform/lang-api/src/com/intellij/openapi/projectRoots/SdkType.java
+++ b/platform/lang-api/src/com/intellij/openapi/projectRoots/SdkType.java
@@ -68,7 +68,7 @@ public abstract class SdkType implements SdkTypeId {
 
   @Override
   @Nullable
-  public String getVersionString(Sdk sdk) {
+  public String getVersionString(@NotNull Sdk sdk) {
     return getVersionString(sdk.getHomePath());
   }
 
@@ -99,15 +99,15 @@ public abstract class SdkType implements SdkTypeId {
 
   @Override
   @Nullable
-  public SdkAdditionalData loadAdditionalData(Sdk currentSdk, Element additional) {
+  public SdkAdditionalData loadAdditionalData(@NotNull Sdk currentSdk, Element additional) {
     return loadAdditionalData(additional);
   }
 
-
-  public SdkType(@NonNls String name) {
+  public SdkType(@NotNull @NonNls String name) {
     myName = name;
   }
 
+  @NotNull
   @Override
   public String getName() {
     return myName;
diff --git a/platform/lang-api/src/com/intellij/openapi/projectRoots/SimpleJavaSdkType.java b/platform/lang-api/src/com/intellij/openapi/projectRoots/SimpleJavaSdkType.java
index 41b587694dbe..9db9794a9b9f 100644
--- a/platform/lang-api/src/com/intellij/openapi/projectRoots/SimpleJavaSdkType.java
+++ b/platform/lang-api/src/com/intellij/openapi/projectRoots/SimpleJavaSdkType.java
@@ -20,6 +20,7 @@ import com.intellij.openapi.project.ProjectBundle;
 import com.intellij.openapi.projectRoots.impl.SdkVersionUtil;
 import org.jdom.Element;
 import org.jetbrains.annotations.NonNls;
+import org.jetbrains.annotations.NotNull;
 
 import java.io.File;
 
@@ -55,24 +56,24 @@ public class SimpleJavaSdkType extends SdkType implements JavaSdkType {
   }
 
   @Override
-  public void saveAdditionalData(SdkAdditionalData additionalData, Element additional) {
+  public void saveAdditionalData(@NotNull SdkAdditionalData additionalData, @NotNull Element additional) {
   }
 
   @Override
-  public String getBinPath(Sdk sdk) {
+  public String getBinPath(@NotNull Sdk sdk) {
     return getConvertedHomePath(sdk) + "bin";
   }
 
   @Override
   @NonNls
-  public String getToolsPath(Sdk sdk) {
+  public String getToolsPath(@NotNull Sdk sdk) {
     final String versionString = sdk.getVersionString();
     final boolean isJdk1_x = versionString != null && (versionString.contains("1.0") || versionString.contains("1.1"));
     return getConvertedHomePath(sdk) + "lib" + File.separator + (isJdk1_x? "classes.zip" : "tools.jar");
   }
 
   @Override
-  public String getVMExecutablePath(Sdk sdk) {
+  public String getVMExecutablePath(@NotNull Sdk sdk) {
     return getBinPath(sdk) + File.separator + VM_EXE_NAME;
   }
 
diff --git a/platform/lang-api/src/com/intellij/openapi/projectRoots/impl/UnknownSdkType.java b/platform/lang-api/src/com/intellij/openapi/projectRoots/impl/UnknownSdkType.java
index 98633e3c3de7..2b06e87d833d 100644
--- a/platform/lang-api/src/com/intellij/openapi/projectRoots/impl/UnknownSdkType.java
+++ b/platform/lang-api/src/com/intellij/openapi/projectRoots/impl/UnknownSdkType.java
@@ -19,6 +19,7 @@ import com.intellij.icons.AllIcons;
 import com.intellij.openapi.project.ProjectBundle;
 import com.intellij.openapi.projectRoots.*;
 import org.jdom.Element;
+import org.jetbrains.annotations.NotNull;
 
 import javax.swing.*;
 import java.util.HashMap;
@@ -35,11 +36,12 @@ public class UnknownSdkType extends SdkType{
   /**
    * @param typeName the name of the SDK type that this SDK serves as a plug for
    */
-  private UnknownSdkType(String typeName) {
+  private UnknownSdkType(@NotNull String typeName) {
     super(typeName);
   }
 
-  public static UnknownSdkType getInstance(String typeName) {
+  @NotNull
+  public static UnknownSdkType getInstance(@NotNull String typeName) {
     UnknownSdkType instance = ourTypeNameToInstanceMap.get(typeName);
     if (instance == null) {
       instance = new UnknownSdkType(typeName);
@@ -86,7 +88,7 @@ public class UnknownSdkType extends SdkType{
   }
 
   @Override
-  public void saveAdditionalData(SdkAdditionalData additionalData, Element additional) {
+  public void saveAdditionalData(@NotNull SdkAdditionalData additionalData, @NotNull Element additional) {
   }
 
   @Override
diff --git a/platform/lang-impl/src/com/intellij/openapi/projectRoots/impl/ProjectJdkTableImpl.java b/platform/lang-impl/src/com/intellij/openapi/projectRoots/impl/ProjectJdkTableImpl.java
index c828e239893f..3a5c3ecf355d 100644
--- a/platform/lang-impl/src/com/intellij/openapi/projectRoots/impl/ProjectJdkTableImpl.java
+++ b/platform/lang-impl/src/com/intellij/openapi/projectRoots/impl/ProjectJdkTableImpl.java
@@ -209,15 +209,15 @@ public class ProjectJdkTableImpl extends ProjectJdkTable implements PersistentSt
 
   @Override
   public SdkTypeId getDefaultSdkType() {
-    return UnknownSdkType.getInstance(null);
+    return UnknownSdkType.getInstance("");
   }
 
   @Override
-  public SdkTypeId getSdkTypeByName(String sdkTypeName) {
+  public SdkTypeId getSdkTypeByName(@NotNull String sdkTypeName) {
     return findSdkTypeByName(sdkTypeName);
   }
 
-  public static SdkTypeId findSdkTypeByName(String sdkTypeName) {
+  public static SdkTypeId findSdkTypeByName(@NotNull String sdkTypeName) {
     final SdkType[] allSdkTypes = SdkType.getAllTypes();
     for (final SdkType type : allSdkTypes) {
       if (type.getName().equals(sdkTypeName)) {
diff --git a/platform/projectModel-api/src/com/intellij/openapi/projectRoots/ProjectJdkTable.java b/platform/projectModel-api/src/com/intellij/openapi/projectRoots/ProjectJdkTable.java
index 0c97fd608661..8fee9a1a98da 100644
--- a/platform/projectModel-api/src/com/intellij/openapi/projectRoots/ProjectJdkTable.java
+++ b/platform/projectModel-api/src/com/intellij/openapi/projectRoots/ProjectJdkTable.java
@@ -19,6 +19,7 @@ import com.intellij.openapi.components.ServiceManager;
 import com.intellij.openapi.util.Comparing;
 import com.intellij.openapi.util.Condition;
 import com.intellij.util.messages.Topic;
+import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import java.util.EventListener;
@@ -88,7 +89,7 @@ public abstract class ProjectJdkTable {
 
   public abstract SdkTypeId getDefaultSdkType();
 
-  public abstract SdkTypeId getSdkTypeByName(String name);
+  public abstract SdkTypeId getSdkTypeByName(@NotNull String name);
 
   public abstract Sdk createSdk(final String name, final SdkTypeId sdkType);
 
diff --git a/platform/projectModel-api/src/com/intellij/openapi/projectRoots/SdkTypeId.java b/platform/projectModel-api/src/com/intellij/openapi/projectRoots/SdkTypeId.java
index b4ff27528aab..bc4fd56a4b93 100644
--- a/platform/projectModel-api/src/com/intellij/openapi/projectRoots/SdkTypeId.java
+++ b/platform/projectModel-api/src/com/intellij/openapi/projectRoots/SdkTypeId.java
@@ -16,19 +16,21 @@
 package com.intellij.openapi.projectRoots;
 
 import org.jdom.Element;
+import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 /**
  * @author yole
  */
 public interface SdkTypeId {
+  @NotNull
   String getName();
 
   @Nullable
-  String getVersionString(Sdk sdk);
+  String getVersionString(@NotNull Sdk sdk);
 
-  void saveAdditionalData(SdkAdditionalData additionalData, Element additional);
+  void saveAdditionalData(@NotNull SdkAdditionalData additionalData, @NotNull Element additional);
 
   @Nullable
-  SdkAdditionalData loadAdditionalData(Sdk currentSdk, Element additional);
+  SdkAdditionalData loadAdditionalData(@NotNull Sdk currentSdk, Element additional);
 }
diff --git a/platform/projectModel-impl/src/com/intellij/core/CoreProjectJdkTable.java b/platform/projectModel-impl/src/com/intellij/core/CoreProjectJdkTable.java
index ef055c0bfc14..7a7e8850d79a 100644
--- a/platform/projectModel-impl/src/com/intellij/core/CoreProjectJdkTable.java
+++ b/platform/projectModel-impl/src/com/intellij/core/CoreProjectJdkTable.java
@@ -19,6 +19,7 @@ import com.intellij.openapi.projectRoots.ProjectJdkTable;
 import com.intellij.openapi.projectRoots.Sdk;
 import com.intellij.openapi.projectRoots.SdkTypeId;
 import com.intellij.openapi.util.Comparing;
+import org.jetbrains.annotations.NotNull;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -99,7 +100,7 @@ public class CoreProjectJdkTable extends ProjectJdkTable {
   }
 
   @Override
-  public SdkTypeId getSdkTypeByName(String name) {
+  public SdkTypeId getSdkTypeByName(@NotNull String name) {
     return CoreSdkType.INSTANCE;
   }
 
diff --git a/platform/projectModel-impl/src/com/intellij/core/CoreSdkType.java b/platform/projectModel-impl/src/com/intellij/core/CoreSdkType.java
index 3beedf6cc5ba..63d86aa87526 100644
--- a/platform/projectModel-impl/src/com/intellij/core/CoreSdkType.java
+++ b/platform/projectModel-impl/src/com/intellij/core/CoreSdkType.java
@@ -19,6 +19,7 @@ import com.intellij.openapi.projectRoots.Sdk;
 import com.intellij.openapi.projectRoots.SdkAdditionalData;
 import com.intellij.openapi.projectRoots.SdkTypeId;
 import org.jdom.Element;
+import org.jetbrains.annotations.NotNull;
 
 /**
  * @author yole
@@ -29,22 +30,23 @@ public class CoreSdkType implements SdkTypeId {
 
   public static CoreSdkType INSTANCE = new CoreSdkType();
 
+  @NotNull
   @Override
   public String getName() {
     return "";
   }
 
   @Override
-  public String getVersionString(Sdk sdk) {
+  public String getVersionString(@NotNull Sdk sdk) {
     return "";
   }
 
   @Override
-  public void saveAdditionalData(SdkAdditionalData additionalData, Element additional) {
+  public void saveAdditionalData(@NotNull SdkAdditionalData additionalData, @NotNull Element additional) {
   }
 
   @Override
-  public SdkAdditionalData loadAdditionalData(Sdk currentSdk, Element additional) {
+  public SdkAdditionalData loadAdditionalData(@NotNull Sdk currentSdk, Element additional) {
     return null;
   }
 }
diff --git a/plugins/devkit/src/projectRoots/IdeaJdk.java b/plugins/devkit/src/projectRoots/IdeaJdk.java
index 6b40ced49796..a958af18d949 100644
--- a/plugins/devkit/src/projectRoots/IdeaJdk.java
+++ b/plugins/devkit/src/projectRoots/IdeaJdk.java
@@ -121,7 +121,7 @@ public class IdeaJdk extends JavaDependentSdkType implements JavaSdkType {
   }
 
   @Nullable
-  public final String getVersionString(final Sdk sdk) {
+  public final String getVersionString(@NotNull final Sdk sdk) {
     final Sdk internalJavaSdk = getInternalJavaSdk(sdk);
     return internalJavaSdk != null ? internalJavaSdk.getVersionString() : null;
   }
@@ -401,13 +401,13 @@ public class IdeaJdk extends JavaDependentSdkType implements JavaSdkType {
   }
 
   @Nullable
-  public String getBinPath(Sdk sdk) {
+  public String getBinPath(@NotNull Sdk sdk) {
     final Sdk internalJavaSdk = getInternalJavaSdk(sdk);
     return internalJavaSdk == null ? null : JavaSdk.getInstance().getBinPath(internalJavaSdk);
   }
 
   @Nullable
-  public String getToolsPath(Sdk sdk) {
+  public String getToolsPath(@NotNull Sdk sdk) {
     final Sdk jdk = getInternalJavaSdk(sdk);
     if (jdk != null && jdk.getVersionString() != null){
       return JavaSdk.getInstance().getToolsPath(jdk);
@@ -416,12 +416,12 @@ public class IdeaJdk extends JavaDependentSdkType implements JavaSdkType {
   }
 
   @Nullable
-  public String getVMExecutablePath(Sdk sdk) {
+  public String getVMExecutablePath(@NotNull Sdk sdk) {
     final Sdk internalJavaSdk = getInternalJavaSdk(sdk);
     return internalJavaSdk == null ? null : JavaSdk.getInstance().getVMExecutablePath(internalJavaSdk);
   }
 
-  public void saveAdditionalData(SdkAdditionalData additionalData, Element additional) {
+  public void saveAdditionalData(@NotNull SdkAdditionalData additionalData, @NotNull Element additional) {
     if (additionalData instanceof Sandbox) {
       try {
         ((Sandbox)additionalData).writeExternal(additional);
@@ -432,7 +432,7 @@ public class IdeaJdk extends JavaDependentSdkType implements JavaSdkType {
     }
   }
 
-  public SdkAdditionalData loadAdditionalData(Sdk sdk, Element additional) {
+  public SdkAdditionalData loadAdditionalData(@NotNull Sdk sdk, Element additional) {
     Sandbox sandbox = new Sandbox(sdk);
     try {
       sandbox.readExternal(additional);