Allow deactivating undefined singleton constant value services

[notaphplover]

Description

• Allow deactivating singleton undefined values

Related Issue

#1519

How Has This Been Tested?

• Tests run successfully.

Types of changes

• Updated docs / Refactor code / Added a tests case (non-breaking change)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• I have updated the changelog.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.53%. Comparing base (d6f09a6) to head (65e9494).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1628   +/-   ##
=======================================
  Coverage   99.53%   99.53%           
=======================================
  Files          50       50           
  Lines        1495     1496    +1     
  Branches      190      192    +2     
=======================================
+ Hits         1488     1489    +1     
  Misses          4        4           
  Partials        3        3           

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