A function that returns its first argument. This function is useful when writing code in the functional style.

function transformer(transformationFn, value) {
  return (transformationFn || angular.identity)(value);
};

// E.g.
function getResult(fn, input) {
  return (fn || angular.identity)(input);
};

getResult(function(n) { return n * 2; }, 21);   // returns 42
getResult(null, 21);                            // returns 21
getResult(undefined, 21);                       // returns 21