<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def validate_is_non_abstract_vertex_type(self, vertex_classname):
 """Validate that a vertex classname corresponds to a non-abstract vertex class."""

        element = self.get_vertex_schema_element_or_raise(vertex_classname)

        if element.abstract:
            raise InvalidClassError(u'Expected a non-abstract vertex class, but {} is abstract'
                                    .format(vertex_classname))