function get() {
	/* eslint-disable no-invalid-this */
	var max;
	if ( isNull( this._xMax ) ) {
		max = getMax( this._xData );
		return ( isNull( max ) ) ? 1.0 : max;
	}
	return this._xMax;
}
Returns the maximum value of the x-axis domain.

@private
@returns {number} maximum value