code: public Type wildLowerBound(Type t) {
          if (t.hasTag(WILDCARD)) {
              WildcardType w = (WildcardType) t;
              return w.isExtendsBound() ? syms.botType : wildLowerBound(w.type);
          }
          else return t;
      }
docs: Get a wildcard's lower bound, returning non-wildcards unchanged.
  @param t a type argument, either a wildcard or a type