Implements opBinaryRight for the "in" operator, such that k in m will resolve to the list of values for key k in the multivalue map m if that key exists, or null if not.
The key to use.
A list of values for the given key, or null if no such key exists.
StringMultiValueMap m; m.add("a", "hello"); assert("a" in m); assert(("a" in m) == ["hello"]); assert("b" !in m); assert(("b" in m) is null);
Implements opBinaryRight for the "in" operator, such that k in m will resolve to the list of values for key k in the multivalue map m if that key exists, or null if not.