fix(crystal): don't send query parameters when parameter is nil

Author: n-rodriguez

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

@@ -130,7 +130,7 @@ module {{moduleName}}
       # query parameters
       query_params = Hash(String, String).new
       {{#queryParams}}
-      query_params["{{{baseName}}}"] = {{#collectionFormat}}@api_client.build_collection_param({{{paramName}}}, :{{{collectionFormat}}}){{/collectionFormat}}{{^collectionFormat}}{{{paramName}}}.to_s unless {{{paramName}}}.nil?{{/collectionFormat}}
+      query_params["{{{baseName}}}"] = {{#collectionFormat}}@api_client.build_collection_param({{{paramName}}}, :{{{collectionFormat}}}) unless {{{paramName}}}.nil?{{/collectionFormat}}{{^collectionFormat}}{{{paramName}}}.to_s unless {{{paramName}}}.nil?{{/collectionFormat}}
       {{/queryParams}}
 
       # header parameters