RUBY-12276: reverting callback API refactoring

platform/core-api/src/com/intellij/lang/PsiBuilder.java

@@ -76,10 +76,8 @@ public interface PsiBuilder extends UserDataHolder, UserDataHolderUnprotected {
   /**
    * Subscribe for notification on default whitespace and comments skipped events.
    * @param callback an implementation for the callback
-   * @return previously registered callback
    */
-  @Nullable
-  WhitespaceSkippedCallback setWhitespaceSkippedCallback(@Nullable WhitespaceSkippedCallback callback);
+  void setWhitespaceSkippedCallback(@Nullable WhitespaceSkippedCallback callback);
 
   /**
    * See what token type is in <code>steps</code> ahead

platform/core-impl/src/com/intellij/lang/impl/PsiBuilderAdapter.java

@@ -62,9 +62,8 @@ public class PsiBuilderAdapter implements PsiBuilder {
   }
 
   @Override
-  @Nullable
-  public WhitespaceSkippedCallback setWhitespaceSkippedCallback(@Nullable final WhitespaceSkippedCallback callback) {
-    return myDelegate.setWhitespaceSkippedCallback(callback);
+  public void setWhitespaceSkippedCallback(@Nullable final WhitespaceSkippedCallback callback) {
+    myDelegate.setWhitespaceSkippedCallback(callback);
   }
 
   @Override

platform/core-impl/src/com/intellij/lang/impl/PsiBuilderImpl.java

@@ -734,11 +734,8 @@ public class PsiBuilderImpl extends UserDataHolderBase implements PsiBuilder {
   }
 
   @Override
-  @Nullable
-  public WhitespaceSkippedCallback setWhitespaceSkippedCallback(@Nullable final WhitespaceSkippedCallback callback) {
-    final WhitespaceSkippedCallback oldCallback = myWhitespaceSkippedCallback;
+  public void setWhitespaceSkippedCallback(@Nullable final WhitespaceSkippedCallback callback) {
     myWhitespaceSkippedCallback = callback;
-    return oldCallback;
   }
 
   @Override