protractor bootstrap validation pop message

Question

I want to do the validation using protractor for bootstrap pop up. I used the below code it ran successfully three times but now its getting null.

element.all(by.css("input:required")).first().getText().then(function(text) {
    console.log(text);
    expect(text.should.be.equal("Please fill out this field."));
})

The pop up is similar to this: https://github.com/angular/protractor/issues/1209