Use NULL over nil for non-object pointer for consistency.

Classes/Utility/FLEXUtility.m

@@ -136,7 +136,7 @@
                                 @"«" : @"«",
                                 @"»" : @"»"
                                 };
-        regex = [NSRegularExpression regularExpressionWithPattern:@"(&|>|<|'|\"|«|»)" options:0 error:nil];
+        regex = [NSRegularExpression regularExpressionWithPattern:@"(&|>|<|'|\"|«|»)" options:0 error:NULL];
     });
     
     NSMutableString *mutableString = [originalString mutableCopy];