Feature Request: add support for querying field where "!=" nil

[dcts]

The javascript firestore SDK supports .where(fieldname, "!=", null) (since version 7.21.0), which is great and a really usefull query. For the ruby sdk I did notice this method is not supported yet. See docs.

Describe the solution you'd like

• add support for db.col.where(fieldname, "!=", nil)

Describe alternatives you've considered

• using the javascript SDK and deploying an API solely for this specific query (time-consuming)
• fetching all documents and filtering them on my server with ruby (costly)

[quartzmo]

@dcts Thank you for opening this issue. I will add the following operators:

• != - a query operator to find documents where a field’s value is set and does not equal the specified value.
• NOT_IN - a query operator to find documents where a field’s value is != any of the values in the specified array.

[quartzmo]

Existing implementations:

• Java PR
• Node PR

[quartzmo]

This feature was released in google-cloud-firestore v2.4.0.