Mockery fails on with() with omitted optional values

mockery-omitted-optional-values.php

class MyClass 
{
  public function doStuff($param, array $optional = []) 
  {
     // some logic
     return true;
  }

}

// this fails
  $myClassMock->shouldReceive('doStuff')
      ->with('some param')
      ->once()
      ->andReturn(true);

// this passes      
  $myClassMock->shouldReceive('doStuff')
      ->with('some param', [])
      ->once()
      ->andReturn(true);