'Returns a user-defined attribute from an asset if it exists; otherwise,
returns None.'

def _asset_get_attribute(self, asset, attrib):

    if ('ATTRIBS' in asset):
        for attrib_block in asset['ATTRIBS'].keys():
            if (attrib in asset['ATTRIBS'][attrib_block]):
                return asset['ATTRIBS'][attrib_block][attrib]
    return None
