try to find a geometry in the provided JSON object

def geometry_from_json(obj):
    '''try to find a geometry in the provided JSON object'''
    obj_type = obj.get('type', None)
    if not obj_type:
        return None
    if obj_type == 'FeatureCollection':
        features = obj.get('features', [])
        if len(features):
            obj = obj['features'][0]
            obj_type = obj.get('type', None)
        else:
            return None
    if obj_type == 'Feature':
        geom = obj['geometry']
    else:
        geom = obj
    # @todo we're just assuming it's a geometry at this point
    if 'coordinates' in geom:
        return geom