fix: check existence of superclass before accessing its name

[cyuyang]

According to the JDK doc, getSuperClass() could return null.

Returns the Class representing the direct superclass of the entity (class, interface, primitive type or void) represented by this Class. If this Class represents either the Object class, an interface, a primitive type, or void, then null is returned. If this object represents an array class then the Class object representing the Object class is returned.
Returns:
the direct superclass of the class represented by this object

In our env, without a null check first, this line caused scanning of parameter types that are interfaces to throw NPE.