Issue 257 - Don't return a String where a Date is required (using generics in Criterion API would prevent this kind of problem, but that's incompatible with the use of the Eval_Error class)

git-svn-id: http://google-refine.googlecode.com/svn/trunk@1933 7d457c2a-affb-35e4-300a-418c747d4874

main/src/com/google/refine/sorting/DateCriterion.java

@@ -56,7 +56,7 @@ public class DateCriterion extends Criterion {
 						return s_error;
 					}
 				}
-				return value;
+				return null;
 			}
 			
 			@Override