fix(crystal): make optional parameters truly optional

Author: n-rodriguez

modules/openapi-generator/src/main/resources/crystal/api.mustache

@@ -23,7 +23,7 @@ module {{moduleName}}
     {{/required}}
     {{/allParams}}
     # @return [{{{returnType}}}{{^returnType}}nil{{/returnType}}]
-    def {{operationId}}({{#allParams}}{{paramName}} : {{{dataType}}}{{^required}}?{{/required}}{{^-last}}, {{/-last}}{{/allParams}})
+    def {{operationId}}({{#allParams}}{{paramName}} : {{{dataType}}}{{^required}}?{{/required}}{{^required}} = nil{{/required}}{{^-last}}, {{/-last}}{{/allParams}})
       {{#returnType}}data, _status_code, _headers = {{/returnType}}{{operationId}}_with_http_info({{#allParams}}{{paramName}}{{^-last}}, {{/-last}}{{/allParams}})
       {{#returnType}}data{{/returnType}}{{^returnType}}nil{{/returnType}}
     end
@@ -40,7 +40,7 @@ module {{moduleName}}
     {{/required}}
     {{/allParams}}
     # @return [Array<({{{returnType}}}{{^returnType}}nil{{/returnType}}, Integer, Hash)>] {{#returnType}}{{{.}}} data{{/returnType}}{{^returnType}}nil{{/returnType}}, response status code and response headers
-    def {{operationId}}_with_http_info({{#allParams}}{{paramName}} : {{{dataType}}}{{^required}}?{{/required}}{{^-last}}, {{/-last}}{{/allParams}})
+    def {{operationId}}_with_http_info({{#allParams}}{{paramName}} : {{{dataType}}}{{^required}}?{{/required}}{{^required}} = nil{{/required}}{{^-last}}, {{/-last}}{{/allParams}})
       if @api_client.config.debugging
         Log.debug {"Calling API: {{classname}}.{{operationId}} ..."}
       end