function processExit( code, signal ) {
		var error;
		if ( err ) {
			return;
		}
		if ( code !== null && code !== 0 ) {
			error = new Error( format( 'unexpected error. Child process failed with exit code: `%u`.', code ) );
		} else if ( signal !== null ) {
			error = new Error( format( 'unexpected error. Child process failed due to termination signal: `%s`.', signal ) );
		}
		if ( error ) {
			error.code = code;
			error.signal = signal;
			return close( error );
		}
	}
Processes process exit values. If provided a non-zero exit code or termination signal, instructs the process to close.

@private
@param {(number|null)} code - exit code
@param {(string|null)} signal - termination signal
@returns {void}