/**
 * Trim a string, removing leading and trailing whitespace
 * @param  {string} input
 * @return {string} trimmed string
 */
PolymerExpressions.prototype.trim = function(input){
	return input.replace(/^\s*|\s*$/g, '');
}
/**
 * Trim a string, removing leading and trailing whitespace
 * @param  {string} input
 * @return {string} trimmed string
 */
PolymerExpressions.prototype.trim = function(input){
  return input && input.replace(/^\s*|\s*$/g, '');
}

Add check to ensure trim does not error
Add check to ensure trim does not error

- checks that input exists before attempting regex
- silences a thrown error
	- seems to keep with spirit of template filters, if value is not provided no need to throw an error
