docs: public TypeDescriptor upcast(Class<?> superType) {
  		if (superType == null) {
  			return null;
  		}
  		Assert.isAssignable(superType, getType());
  		return new TypeDescriptor(superType, this.elementTypeDescriptor,
  				this.mapKeyTypeDescriptor, this.mapValueTypeDescriptor, this.annotations);
  	}