code: public static ResolvableType forMethodReturnType(Method method, Class<?> implementationClass) {
  		Assert.notNull(method, "Method must not be null");
  		MethodParameter methodParameter = MethodParameter.forMethodOrConstructor(method, -1);
  		methodParameter.setContainingClass(implementationClass);
  		return forMethodParameter(methodParameter);
  	}
docs: Return a {@link ResolvableType} for the specified {@link Method} return type.
  Use this variant when the class that declares the method includes generic
  parameter variables that are satisfied by the implementation class.
  @param method the source for the method return type
  @param implementationClass the implementation class
  @return a {@link ResolvableType} for the specified method return
  @see #forMethodReturnType(Method)