getReturns() throw error: Object of class DateTime could not be converted to string

[meditatorzhang]

#0 \\vendor\\highsidelabs\\walmart-api\\src\\ObjectSerializer.php(567): GuzzleHttp\\Psr7\\Query::build(Array, 2)
#1 \\vendor\\highsidelabs\\walmart-api\\src\\Apis\\MP\\US\\ReturnsApi.php(811): Walmart\\ObjectSerializer::buildQuery(Array)
#2 \\vendor\\highsidelabs\\walmart-api\\src\\Apis\\MP\\US\\ReturnsApi.php(446): Walmart\\Apis\\MP\\US\\ReturnsApi->getReturnsRequest(NULL, NULL, NULL, NULL, NULL, NULL, NULL, Object(DateTime), Object(DateTime), '199')
#3 \\vendor\\highsidelabs\\walmart-api\\src\\Apis\\MP\\US\\ReturnsApi.php(411): Walmart\\Apis\\MP\\US\\ReturnsApi->getReturnsWithHttpInfo(NULL, NULL, NULL, NULL, NULL, NULL, NULL, Object(DateTime), Object(DateTime), '199')

I have found this error and fix it.
file: \src\Apis\MP\US\ReturnsApi.php

 ObjectSerializer::toQueryValue(
      $returnLastModifiedStartDate,
      'returnLastModifiedStartDate', // param base name
      'string', // openApiType
      'form', // style
      true, // explode
      false // required
  ) ?? [],
  ObjectSerializer::toQueryValue(
      $returnLastModifiedEndDate,
      'returnLastModifiedEndDate', // param base name
      'string', // openApiType
      'form', // style
      true, // explode
      false // required
  ) ?? [],

modify to:

 ObjectSerializer::toQueryValue(
      $returnLastModifiedStartDate,
      'returnLastModifiedStartDate', // param base name
      '\DateTime', // openApiType
      'form', // style
      true, // explode
      false // required
  ) ?? [],
  ObjectSerializer::toQueryValue(
      $returnLastModifiedEndDate,
      'returnLastModifiedEndDate', // param base name
      '\DateTime', // openApiType
      'form', // style
      true, // explode
      false // required
  ) ?? [],