@Nullable

platform/core-api/src/com/intellij/openapi/fileEditor/FileDocumentManager.java

@@ -34,6 +34,7 @@ public abstract class FileDocumentManager implements SavingRequestor {
   @Nullable
   public abstract Document getCachedDocument(@NotNull VirtualFile file);
 
+  @Nullable
   public abstract VirtualFile getFile(@NotNull Document document);
 
   public abstract void saveAllDocuments();

platform/platform-api/src/com/intellij/openapi/wm/WindowManager.java

@@ -78,6 +78,7 @@ public abstract class WindowManager {
    * @param project
    * @return
    */
+  @Nullable
   public abstract StatusBar getStatusBar(Project project);
 
   /**

platform/platform-impl/src/com/intellij/openapi/fileEditor/impl/FileDocumentManagerImpl.java

@@ -186,6 +186,7 @@ public class FileDocumentManagerImpl extends FileDocumentManager implements Appl
     }
   }
 
+  @Nullable
   public VirtualFile getFile(@NotNull Document document) {
     return document.getUserData(FILE_KEY);
   }

platform/platform-impl/src/com/intellij/openapi/wm/impl/WindowManagerImpl.java

@@ -438,6 +438,7 @@ public final class WindowManagerImpl extends WindowManagerEx implements Applicat
     return myWindowWatcher.suggestParentWindow(project);
   }
 
+  @Nullable
   public final StatusBar getStatusBar(final Project project) {
     if (!myProject2Frame.containsKey(project)) {
       return null;