Filters which are nullable or "possibly undefined" should have a toggle that enables or disables them

[kminehart]

Problem: When changing inputs from populated to empty, the query fails to complete.

Reproducing:

Step 1: Search for issues with a valid assignee.

Step 2: Removing the content from the "assignee" field should result in an error:

Could not find an assignee with the login ''

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This is caused by the behavior of the omitempty flag on the IssueFilters type.

For more information on omitempty: https://golang.org/pkg/encoding/json/

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Solution: Filters which are nullable or "possibly undefined" should have a toggle that enables or disables them.