_getFormElement(formElement = null) {
        let formElementToUse;
        if (!AutoNumericHelper.isNull(formElement)) {
            formElementToUse = formElement;
        } else {
            formElementToUse = this.parentForm;
        }

        return formElementToUse;
    }
Return the given form element, or defaults to `this.parentForm` if no argument is passed.

@param {HTMLFormElement|null} formElement
@returns {*}
@private