BigQueryV2: Allow passing an empty array as a value for params

[knu]

Currently passing an empty array causes the following error:

NoMethodError: undefined method `parameter_type' for nil:NilClass

This is due to Convert.to_query_param trying to use the type of the first element as array_type without checking if a given array has an element.

This PR adds the necessary check.

[quartzmo]

@knu Thank you for submitting this pull request!

[quartzmo]

Related issue in google-cloud-java? googleapis/google-cloud-java#2678

[blowmage]

Thank you for your pull request. Unfortunately we have addressed this issue in a different manner. After discussions with the BigQuery team we have decided to add an optional types argument. This new argument is used to specify the type of a query parameter when one can't be determined. So while PR has elected to use STRING when a type can't be determined, users will have to specify this as follows:

data = dataset.query "SELECT name FROM my_table " \
                     "WHERE url IN UNNEST(@urls)",
                     params: { urls: [] },
                     types: { urls: [:STRING] }

Users are also able to specify a non-STRING array:

data = dataset.query "SELECT name FROM my_table " \
                     "WHERE id IN UNNEST(@ids)",
                     params: { ids: [] },
                     types: { ids: [:INT64] }

[quartzmo]

@pdfabbro Did you intend to post this comment regarding googleapis/nodejs-bigquery here on a googleapis/google-cloud-ruby PR?

[quartzmo]

I think maybe you should post it here? Sorry if I'm not understanding something about how this is relevant to the Ruby client.

https://github.com/googleapis/nodejs-bigquery/issues

[quartzmo]

Great, thanks. I'll verify your observations with the Ruby client and open a new issue for this repo (a sibling to the nodejs repo) if needed. Appreciate the heads up!

[quartzmo]

The new issue related to null parameter values is googleapis/nodejs-bigquery#915.