EA-37261: (code cleanup) PsiDocumentManager.getDocument() returns @Nullable value

platform/core-api/src/com/intellij/psi/PsiDocumentManager.java

@@ -72,6 +72,7 @@ public abstract class PsiDocumentManager {
    * @param file the file for which the document is requested.
    * @return the document instance, or <code>null</code> if the file is binary or has no associated document.
    */
+  @Nullable
   public abstract Document getDocument(@NotNull PsiFile file);
 
   /**

platform/lang-impl/src/com/intellij/psi/impl/PsiDocumentManagerImpl.java

@@ -203,6 +203,7 @@ public class PsiDocumentManagerImpl extends PsiDocumentManager implements Projec
     return ((PsiManagerEx)myPsiManager).getFileManager().findFile(virtualFile);
   }
 
+  @Nullable
   @Override
   public Document getDocument(@NotNull PsiFile file) {
     if (file instanceof PsiBinaryFile) return null;