Prevent NullPointerException when Atlas Vertex is empty because of corrupted data.

Because of corrupted data, there may be a chance of having AtlasVertex as an empty, which means AtlasVertex does not have any property present in it.
This can cause NullPointerException while populating System attributes as well Normal attributes for AtlasEntity object.
To avoid NullPointerException we need to skip such vertices, so that they cannot be used to populate system attributes and normal attributes.