Don't call moveParagraph() with null |VisiblePositon|

Source/core/editing/IndentOutdentCommand.cpp

Index: Source/core/editing/IndentOutdentCommand.cpp
diff --git a/Source/core/editing/IndentOutdentCommand.cpp b/Source/core/editing/IndentOutdentCommand.cpp
index c37dd3c63ee08da3a97ee3888fae6a3f1d01c073..3b0963ed29ce004492186b0654859f65d818502e 100644
--- a/Source/core/editing/IndentOutdentCommand.cpp
+++ b/Source/core/editing/IndentOutdentCommand.cpp
@@ -185,9 +185,13 @@ void IndentOutdentCommand::outdentParagraph()
         Node* highestInlineNode = highestEnclosingNodeOfType(visibleStartOfParagraph.deepEquivalent(), isInline, CannotCrossEditingBoundary, enclosingBlockFlow);
         splitElement(toElement(enclosingNode), (highestInlineNode) ? highestInlineNode : visibleStartOfParagraph.deepEquivalent().deprecatedNode());
     }
+    VisiblePosition startOfParagraphToMove(startOfParagraph(visibleStartOfParagraph));
+    VisiblePosition endOfParagraphToMove(endOfParagraph(visibleEndOfParagraph));
+    if (startOfParagraphToMove.isNull() || endOfParagraphToMove.isNull())
+        return;
     RefPtrWillBeRawPtr<Node> placeholder = createBreakElement(document());
     insertNodeBefore(placeholder, splitBlockquoteNode);
-    moveParagraph(startOfParagraph(visibleStartOfParagraph), endOfParagraph(visibleEndOfParagraph), VisiblePosition(positionBeforeNode(placeholder.get())), true);
+    moveParagraph(startOfParagraphToMove, endOfParagraphToMove, VisiblePosition(positionBeforeNode(placeholder.get())), true);
 }
 
 // FIXME: We should merge this function with ApplyBlockElementCommand::formatSelection