public function testEqualEmpty()
 {
     $filter = new Filter();
     $filter->setFromColumn($this->column, '=');
     $this->assertEquals(Filter::EQUAL, $filter->getOperator());
     $this->assertEquals('= ', $filter->getDisplayColumnValue());
     $this->assertTrue(is_array($filter->getValues()));
     $this->assertEquals(array(''), $filter->getValues());
     $this->assertTrue($filter->isColumnFilter());
 }