Spock: mock a method with varargs

This question is an offshoot of this Q&A: Test Groovy class that uses System.console()

The problem:

Spock framework incorrectly checks arguments of the mocked method with varargs.

Steps to reproduce:

1) Create groovy project

2) Create an interface:

interface IConsole {
  String readLine(String fmt, Object ... args)
}

3) Create spock test:

class TestInputMethods extends Specification {

  def 'test console input'() {
    setup:
    def consoleMock = GroovyMock(IConsole)
    1 * consoleMock.readLine(_) >> 'validResponse'

    when:
    // here we get exception "wrong number of arguments":
    def testResult = consoleMock.readLine('testPrompt')

    then:
    testResult == 'validResponse'
  }
}

4) try running the test

Effect: test fails with exception "wrong number of arguments".

Workaround:

call to readLine is replaced with:

def testResult = consoleMock.readLine('testPrompt', [] as Object[])

then test completes successfully.

Question:

is there a better way to "explain" spock that the last argument of the mocked function is vararg and, as such, it could be omitted?