function set( num ) {
	/* eslint-disable no-invalid-this */
	var err = isValid( num );
	if ( err ) {
		throw err;
	}
	debug( 'Current value: %d.', num );

	this._numTicks = num;
	debug( 'New Value: %s.', this._numTicks );

	this.emit( CHANGE_EVENT );
}
Sets the number of axis ticks.

@private
@param {(NonNegativeInteger|null)} num - num
@throws {TypeError} must be a nonnegative integer or null