Twitter bootstrap 3 boostrapvalidator文本区域验证始终为绿色

我有这个区号：

<div class="col-md-10">
<textarea class="form-control" cols="20" id="Op_Question" name="Op_Question" rows="2" data-bv-field="Op_Question"></textarea>
</div>

问题是，引导验证程序总是绿色的，即使文本区域是空的，为什么会发生这种情况

干杯

            Op_Question: {
                validators: {
                    notEmpty: {
                        message: 'The Question is required and cannot be empty'
                    },
                    stringLength: {
                        max: 500,
                        message: 'Post content must be less than 120 characters'
                    }
                }
            }