* FieldDisplay: added support for value mapping of no data state.
Committer: Marcus Andersson <marcus.andersson@grafana.com>
* FieldDisplay: fixed issue when switching between modes and display numeric was null.
* ValueMapping: introduced a private function for checking null values.
* FieldDisplay: refactoring of test setup to reduce duplication.
* Docs: added info about new 'no data' value to text mapping.
* Docs: improved according to feedback. Reverted prettier formatting changes.
* FieldDisplay: removed unused import.