Enhancement: Implement NullProvider

[localheinz]

This PR

• implements DataProvider\NullProvider

Follows #326.

[codecov]

Codecov Report

Merging #327 into main will decrease coverage by 1.99%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##               main     #327      +/-   ##
============================================
- Coverage     92.85%   90.86%   -2.00%     
- Complexity       56       57       +1     
============================================
  Files             6        7       +1     
  Lines           182      186       +4     
============================================
  Hits            169      169              
- Misses           13       17       +4     

Impacted Files	Coverage Δ	Complexity Δ
src/DataProvider/NullProvider.php	0.00% <0.00%> (ø)	1.00 <1.00> (?)

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