Actually we can't set it to null (then calling method can't identify the method to call).  But we can set it to something like
new  WrappedType() at the calling method.

In message receiver also we have

ReturnType paramx = null;

WrappedType wrappedParam = formOM(...);

InterType1 param1 = getMethod1(wrappedParam);
InterType2 param2 = getMethod2(wrappedParam);

paramx = skel.getMethod(param1,param2);

Here param1 and param2 always param1, param2 since it is the position in the loop for loop.
So if paramx is equal to either the param1 or param2 then also we get a compilation problem.

Shall we remove the param1, param2 terms as follows

paramx = skel.getMethod(getMethod1(wrappedParam), getMethod2(wrappedParam));