stac generation fails if mcf has no 'pointofcontact'

/schemas/stac/__init__.py", line 125, in write
    stac_item['properties']['providers'] = [{'name': mcf['contact']['pointOfContact']['organization']}]

TypeError: 'NoneType' object is not subscriptable

https://github.com/geopython/pygeometa/blob/42273bdeb602cb344f1f4c9d05fdc40784e62468/pygeometa/schemas/stac/__init__.py#L127