NullPointerException in EnumSelectModel for invalid PropertyModel

This can be reproduced with the following code snippet:

    Class c = String.class;
    new EnumSelectModel(c, new MapMessages(Locale.US, Collections.emptyMap()));

It happens in org.apache.tapestry5.corelib.pages.PropertyEditBlocks.getSelectModelForProperty() if a PropertyModel has an enum datatype but the PropertyConduit returns a non-enum class from its getPropertyType() method.
Of course, that's a user error, but we should be nice and report a better exception.
There should be checks in EnumSelectModel as well as in PropertyEditBlocks.