Typeahead updater

Small change so that if the typeahead updater returns `undefined` it will no longer wipe out the input value. This allows much greater flexibility to work with the typeahead. 

My use is for an address auto completion field - but when the address is selected the updater is mapping the different parts of the address to separate input fields and sets the values, further having no return. Currently that will wipe out the value I set in the input.