Index: parser/Parser.php
===================================================================
--- parser/Parser.php	(revision 102411)
+++ parser/Parser.php	(working copy)
@@ -2834,12 +2834,10 @@
 				global $wgLanguageCode;
 				return $wgLanguageCode;
 			default:
-				$ret = null;
-				if ( wfRunHooks( 'ParserGetVariableValueSwitch', array( &$this, &$this->mVarCache, &$index, &$ret, &$frame ) ) ) {
-					return $ret;
-				} else {
-					return null;
-				}
+				// allow extensions to register variables:
+				$ret = null; // null implies no variable found
+				wfRunHooks( 'ParserGetVariableValueSwitch', array( &$this, &$this->mVarCache, &$index, &$ret, &$frame ) );
+				return $ret;
 		}
 
 		if ( $index ) {