function incrnanstdev( mean ) {
	var stdev;
	if ( arguments.length ) {
		stdev = incrstdev( mean );
	} else {
		stdev = incrstdev();
	}
	return accumulator;

	/**
	* If provided a value, the accumulator function returns an updated corrected sample standard deviation. If not provided a value, the accumulator function returns the current corrected sample standard deviation.
	*
	* @private
	* @param {number} [x] - new value
	* @returns {(number|null)} corrected sample standard deviation or null
	*/
	function accumulator( x ) {
		if ( arguments.length === 0 || isnan( x ) ) {
			return stdev();
		}
		return stdev( x );
	}
}
Returns an accumulator function which incrementally computes a corrected sample standard deviation, ignoring `NaN` values.

@param {number} [mean] - mean value
@throws {TypeError} must provide a number
@returns {Function} accumulator function

@example
var accumulator = incrnanstdev();

var s = accumulator();
// returns null

s = accumulator( 2.0 );
// returns 0.0

s = accumulator( -5.0 );
// returns ~4.95

s = accumulator( NaN );
// returns ~4.95

s = accumulator();
// returns ~4.95

@example
var accumulator = incrnanstdev( 3.0 );