grails spock test mock CommonsMultipartFile

I've following old method written in code, which is for accessing request object in service class such as:

def someServiceMethod() {
  ....
  def webUtils = WebUtils.retrieveGrailsWebRequest()
  def request = webUtils.getCurrentRequest()
  MultipartHttpServletRequest mpr = (MultipartHttpServletRequest) request
  CommonsMultipartFile file = (CommonsMultipartFile) mpr.getFile("file")
  ....
}

This is my unit test code for serivce class.

@TestFor(SomeService)
class SomeServiceSpec extends Specification {
  void "test someServiceMethod"() {
    given:
    MockMultipartHttpServletRequest request = new MockMultipartHttpServletRequest()

    FileInputStream inFile = new FileInputStream("./test-data/Hiearchy-003.xlsx") //valid file path
    def multipartFile = new GrailsMockMultipartFile('file', 'file.xls', 'multipart/form-data', inFile)
    request.addFile(multipartFile)
    GrailsWebRequest webRequest = new GrailsWebRequest(
            request,
            new MockHttpServletResponse(),
            new MockServletContext()
    )
    request.setAttribute(GrailsApplicationAttributes.WEB_REQUEST,webRequest)
    RequestContextHolder.setRequestAttributes(webRequest);

    when:
    def result = service.someServiceMethod()

    then:
    result != null
    //some more assertions
    //..
  }
}

I'm stuck with following error.

| Failure:  test someServiceMethod(SomeServiceSpec)
|  org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object 'org.codehaus.groovy.grails.plugins.testing.GrailsMockMultipartFile@6ae8e5dd' with class 'org.codehaus.groovy.grails.plugins.testing.GrailsMockMultipartFile' to class 'org.springframework.web.multipart.commons.CommonsMultipartFile'

Anybody faced such issue before in grails unit test?