fixes data/ not being properly updated if a query update is null

[reimertz]

Description

Previously, when doing queries like below, if userId was removed from the invitees array, data was not properly updated. With this PR, data is properly updated.

firestoreConnect(props=> [{
      collection: 'events',
      populates,
      where: [
        ['invitees', 'array-contains', props.currentUser.uid],
      ],
      storeAs: 'events_invited'
    }]
)

Check List

If not relevant to pull request, check off as complete

• [ x ] All tests passing
• [ ? ] Docs updated with any changes or examples if applicable
• [ ? ] Added tests to ensure new feature(s) work properly

[reimertz]

On a second though, since I use storeAs, this might be the reason why nothing breaks when applying this fix?