diff --git a/platform/core-api/src/com/intellij/psi/ExternallyAnnotated.java b/platform/core-api/src/com/intellij/psi/ExternallyAnnotated.java
index ed0adde37cfd..a18202feea7a 100644
--- a/platform/core-api/src/com/intellij/psi/ExternallyAnnotated.java
+++ b/platform/core-api/src/com/intellij/psi/ExternallyAnnotated.java
@@ -8,19 +8,20 @@ import org.jetbrains.annotations.Nullable;
  * Helper interface for PSI elements which may be added as ForeignLeaf and need to redirect annotations
  * to another text range.
  */
+@FunctionalInterface
 public interface ExternallyAnnotated {
   /**
    * If inspection started for files with ForeignLeaf substitutions founds any problem in them
-   * it should be able to display them locally. This method allows to define such substitution text range.
+   * it should be able to display it locally. This method allows to define such substitution text range.
    * An example from C/C++ macro substitution:<br/><pre>
    * #define T(x) int x
    * int k;
-   * T(k) = 0; // the problem [duplicate declaration 'k'] need to be annotated
+   * T(k) = 0; // the problem [duplicate declaration 'k'] needs to be annotated
    *           // for macro parameter, not declarator
    * </pre><br/>
-   * See {@code ProblemDescriptorBase} constructor for details.
+   * See {@link com.intellij.codeInspection.ProblemDescriptorBase} constructor for details.
    *
-   * @return TextRange to which problem descriptions should be redirected, {@code null} if annotator need to skip the problem
+   * @return TextRange to which problem descriptions should be redirected, {@code null} if annotator needs to skip the problem
    */
   @Nullable
   TextRange getAnnotationRegion();
diff --git a/platform/core-api/src/com/intellij/psi/impl/ElementBase.java b/platform/core-api/src/com/intellij/psi/impl/ElementBase.java
index 604aaa4d52c7..34a95dc746dc 100644
--- a/platform/core-api/src/com/intellij/psi/impl/ElementBase.java
+++ b/platform/core-api/src/com/intellij/psi/impl/ElementBase.java
@@ -85,10 +85,7 @@ public abstract class ElementBase extends UserDataHolderBase implements Iconable
     try {
       return computeIcon(flags);
     }
-    catch (ProcessCanceledException e) {
-      throw e;
-    }
-    catch (IndexNotReadyException e) {
+    catch (ProcessCanceledException | IndexNotReadyException e) {
       throw e;
     }
     catch (Exception e) {
diff --git a/platform/core-impl/src/com/intellij/psi/DummyHolderViewProvider.java b/platform/core-impl/src/com/intellij/psi/DummyHolderViewProvider.java
index 32bc8e76c8ff..5652219361a7 100644
--- a/platform/core-impl/src/com/intellij/psi/DummyHolderViewProvider.java
+++ b/platform/core-impl/src/com/intellij/psi/DummyHolderViewProvider.java
@@ -70,6 +70,7 @@ public class DummyHolderViewProvider extends AbstractFileViewProvider {
     return target == getBaseLanguage() ? myHolder : null;
   }
 
+  @NotNull
   @Override
   public List<PsiFile> getCachedPsiFiles() {
     return Collections.singletonList(myHolder);
diff --git a/platform/core-impl/src/com/intellij/psi/MultiplePsiFilesPerDocumentFileViewProvider.java b/platform/core-impl/src/com/intellij/psi/MultiplePsiFilesPerDocumentFileViewProvider.java
index e1e776c8e587..dcfa24bcb800 100644
--- a/platform/core-impl/src/com/intellij/psi/MultiplePsiFilesPerDocumentFileViewProvider.java
+++ b/platform/core-impl/src/com/intellij/psi/MultiplePsiFilesPerDocumentFileViewProvider.java
@@ -29,7 +29,6 @@ import com.intellij.psi.impl.source.PsiFileImpl;
 import com.intellij.psi.impl.source.tree.FileElement;
 import com.intellij.psi.templateLanguages.OuterLanguageElement;
 import com.intellij.util.ConcurrencyUtil;
-import com.intellij.util.NullableFunction;
 import com.intellij.util.ReflectionUtil;
 import com.intellij.util.containers.ContainerUtil;
 import org.jetbrains.annotations.NotNull;
@@ -41,9 +40,9 @@ import java.util.concurrent.ConcurrentMap;
 
 public abstract class MultiplePsiFilesPerDocumentFileViewProvider extends AbstractFileViewProvider {
   private final ConcurrentMap<Language, PsiFileImpl> myRoots = ContainerUtil.newConcurrentMap(1, 0.75f, 1);
-  private MultiplePsiFilesPerDocumentFileViewProvider myOriginal = null;
+  private MultiplePsiFilesPerDocumentFileViewProvider myOriginal;
 
-  public MultiplePsiFilesPerDocumentFileViewProvider(PsiManager manager, VirtualFile virtualFile, boolean eventSystemEnabled) {
+  public MultiplePsiFilesPerDocumentFileViewProvider(@NotNull PsiManager manager, @NotNull VirtualFile virtualFile, boolean eventSystemEnabled) {
     super(manager, virtualFile, eventSystemEnabled, virtualFile.getFileType());
   }
 
@@ -67,7 +66,7 @@ public abstract class MultiplePsiFilesPerDocumentFileViewProvider extends Abstra
     return roots;
   }
 
-  protected final void removeFile(final Language language) {
+  protected final void removeFile(@NotNull Language language) {
     PsiFileImpl file = myRoots.remove(language);
     if (file != null) {
       file.markInvalidated();
@@ -108,9 +107,10 @@ public abstract class MultiplePsiFilesPerDocumentFileViewProvider extends Abstra
     return myRoots.get(target);
   }
 
+  @NotNull
   @Override
   public final List<PsiFile> getCachedPsiFiles() {
-    return ContainerUtil.mapNotNull(myRoots.keySet(), (NullableFunction<Language, PsiFile>)language -> getCachedPsi(language));
+    return ContainerUtil.mapNotNull(myRoots.keySet(), this::getCachedPsi);
   }
 
   @NotNull
@@ -148,7 +148,8 @@ public abstract class MultiplePsiFilesPerDocumentFileViewProvider extends Abstra
     return copy;
   }
 
-  protected abstract MultiplePsiFilesPerDocumentFileViewProvider cloneInner(VirtualFile fileCopy);
+  @NotNull
+  protected abstract MultiplePsiFilesPerDocumentFileViewProvider cloneInner(@NotNull VirtualFile fileCopy);
 
   @Override
   @Nullable
diff --git a/platform/core-impl/src/com/intellij/psi/SingleRootFileViewProvider.java b/platform/core-impl/src/com/intellij/psi/SingleRootFileViewProvider.java
index e8794cbda9f0..a29e6b97a0e3 100644
--- a/platform/core-impl/src/com/intellij/psi/SingleRootFileViewProvider.java
+++ b/platform/core-impl/src/com/intellij/psi/SingleRootFileViewProvider.java
@@ -149,6 +149,7 @@ public class SingleRootFileViewProvider extends AbstractFileViewProvider impleme
     return file == PsiUtilCore.NULL_PSI_FILE ? null : file;
   }
 
+  @NotNull
   @Override
   public final List<PsiFile> getCachedPsiFiles() {
     return ContainerUtil.createMaybeSingletonList(getCachedPsi(getBaseLanguage()));
@@ -219,7 +220,6 @@ public class SingleRootFileViewProvider extends AbstractFileViewProvider impleme
     return contentSize > PersistentFSConstants.getMaxIntellisenseFileSize();
   }
 
-  @SuppressWarnings("UnusedParameters")
   public static boolean isTooLargeForContentLoading(@NotNull VirtualFile vFile, final long contentSize) {
     return contentSize > PersistentFSConstants.FILE_LENGTH_TO_CACHE_THRESHOLD;
   }
diff --git a/platform/util/src/com/intellij/openapi/util/TextRange.java b/platform/util/src/com/intellij/openapi/util/TextRange.java
index fa94e2805101..83934550169c 100644
--- a/platform/util/src/com/intellij/openapi/util/TextRange.java
+++ b/platform/util/src/com/intellij/openapi/util/TextRange.java
@@ -193,8 +193,9 @@ public class TextRange implements Segment, Serializable {
 
   @Nullable
   public TextRange intersection(@NotNull TextRange range) {
-    if (!intersects(range)) return null;
-    return new TextRange(Math.max(myStartOffset, range.getStartOffset()), Math.min(myEndOffset, range.getEndOffset()));
+    int newStart = Math.max(myStartOffset, range.getStartOffset());
+    int newEnd = Math.min(myEndOffset, range.getEndOffset());
+    return isProperRange(newStart, newEnd) ? new TextRange(newStart, newEnd) : null;
   }
 
   public boolean isEmpty() {
@@ -224,8 +225,12 @@ public class TextRange implements Segment, Serializable {
   }
 
   public static void assertProperRange(int startOffset, int endOffset, @NotNull Object message) {
-    if (startOffset > endOffset || startOffset < 0) {
+    if (!isProperRange(startOffset, endOffset)) {
       LOG.error("Invalid range specified: (" + startOffset + "," + endOffset + "); " + message);
     }
   }
+
+  private static boolean isProperRange(int startOffset, int endOffset) {
+    return startOffset <= endOffset && startOffset >= 0;
+  }
 }
diff --git a/python/python-rest/src/com/jetbrains/rest/RestFileViewProvider.java b/python/python-rest/src/com/jetbrains/rest/RestFileViewProvider.java
index 4b7bfb1b90f8..44b2ed16ae82 100644
--- a/python/python-rest/src/com/jetbrains/rest/RestFileViewProvider.java
+++ b/python/python-rest/src/com/jetbrains/rest/RestFileViewProvider.java
@@ -54,8 +54,9 @@ public class RestFileViewProvider extends MultiplePsiFilesPerDocumentFileViewPro
     return PythonLanguage.getInstance();
   }
 
+  @NotNull
   @Override
-  protected MultiplePsiFilesPerDocumentFileViewProvider cloneInner(VirtualFile virtualFile) {
+  protected MultiplePsiFilesPerDocumentFileViewProvider cloneInner(@NotNull VirtualFile virtualFile) {
     return new RestFileViewProvider(getManager(), virtualFile, false);
   }