json_encode to have a string expression

[koriym]

Closes #252

[codecov]

Codecov Report

Merging #253 (5af43a6) into 1.x (53c2c4b) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 5af43a6 differs from pull request most recent head a2a09fc. Consider uploading reports for the commit a2a09fc to get more accurate results

@@             Coverage Diff             @@
##                 1.x      #253   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity       510       510           
===========================================
  Files             83        83           
  Lines           1308      1308           
===========================================
  Hits            1308      1308           

Impacted Files	Coverage Δ
src/AbstractRequest.php	100.00% <ø> (ø)
...c/JsonSchema/Interceptor/JsonSchemaInterceptor.php	100.00% <100.00%> (ø)

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