support empty array

[koxudaxi]

This PR supports empty array on JsonSchema

Related issues

#111

[codecov]

Codecov Report

Merging #113 into master will not change coverage by %.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #113   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           12        12           
  Lines          865       865           
  Branches       178       178           
=========================================
  Hits           865       865           

Impacted Files	Coverage Δ
datamodel_code_generator/model/pydantic/types.py	100.00% <ø> (ø)
datamodel_code_generator/parser/jsonschema.py	100.00% <100.00%> (ø)

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