If you attempt to register an extension with psycopg2 and happen to use the newrelic python client library you may get an error that looks like this
File "/opt/balanced/embedded/lib/python2.7/site-packages/psycopg2/_json.py", line 142, in register_default_json
loads=loads, oid=JSON_OID, array_oid=JSONARRAY_OID)
File "/opt/balanced/embedded/lib/python2.7/site-packages/psycopg2/_json.py", line 125, in register_json
register_type(JSON, not globally and conn_or_curs or None)
TypeError: argument 2 must be a connection, cursor or None