formvalue(section_id) {
		const elem = this.getUIElement(section_id);
		return elem ? elem.getValue() : null;
	}
Query the current form input value.

The default implementation of this method returns the current input
value of the underlying [LuCI.ui]{@link LuCI.ui.AbstractElement} widget.
It may be overridden by user code to handle input values differently.

@param {string} section_id
The configuration section ID

@throws {TypeError}
Throws a `TypeError` exception when no `section_id` was specified.

@returns {*}
Returns the current input value.