Handle no maturity level & no server

[rjawesome]

biothings/biothings_explorer#572

[codecov]

Codecov Report

Merging #72 (029aaa5) into main (355222e) will decrease coverage by 0.36%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #72      +/-   ##
==========================================
- Coverage   86.53%   86.18%   -0.36%     
==========================================
  Files          30       30              
  Lines         728      731       +3     
  Branches      145      148       +3     
==========================================
  Hits          630      630              
- Misses         97      100       +3     
  Partials        1        1              

Impacted Files	Coverage Δ
src/operations_builder/base_operations_builder.ts	88.23% <100.00%> (+0.73%)	⬆️
src/parser/index.ts	75.55% <100.00%> (-2.86%)	⬇️

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