Constraint for enum in structural search and replace

What constraints in strutural search and replace I must use to match an enum?

I want to find all java.util.Map whose key is an enum. So I have in the search searchtemplate "Map<$keyClass$, $valueClass$> $mapName$ = new HashMap();".

For keyClass I tried the expression constraint "Text/regexp constraint for java expression type" with the value "enum" but without success.