[Bug] BigQuery connector returns None rather than empty Table on query with no rows returned

[austinweisgrau]

The Redshift connector, on running a query that returns no rows, will return a parsons Table with no rows but with all of the columns defined. The BigQuery connector instead returns None.

I like the Redshift connector behavior better - it's more useful to still have the columns named even if there are no rows, and makes using the output from the connector the same whether or not rows are returned, making downstream use easier without conditionals.

Detailed Description

To Reproduce

redshift_tbl = Redshift().query('select current_user limit 0')
type(redshift_tbl)
>> parsons.etl.table.Table
redshift_tbl.columns
>> ['current_user']

bigquery_tbl = BigQuery().query('select session_user() limit 0')
type(bigquery_tbl)
>> NoneType

Your Environment

• Version of Parsons used (if you know):
• Environment name and version (e.g. Chrome 39, node.js 5.4):
• Operating System and version (desktop or mobile):

Additional Context

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