Fix: Populate referenced embeddables

[localheinz]

This PR

• asserts that referenced embeddables are populated
• excludes fields using dot notation

[codecov]

Codecov Report

Merging #79 into master will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master      #79      +/-   ##
============================================
+ Coverage     93.46%   93.53%   +0.06%     
  Complexity       76       76              
============================================
  Files             8        8              
  Lines           199      201       +2     
============================================
+ Hits            186      188       +2     
  Misses           13       13              

Impacted Files	Coverage Δ	Complexity Δ
src/EntityDef.php	95.55% <100.00%> (+0.20%)	13.00 <0.00> (ø)

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