docs(filterFilter): mark the comparator parameter as optional

Mark the `comparator` parameter as optional and mention that it defaults to `false`.

Fixes #15312

Closes #15371

Author: kylewuolle

src/ng/filter/filter.js

@@ -41,7 +41,7 @@
  *
  *     The final result is an array of those elements that the predicate returned true for.
  *
- * @param {function(actual, expected)|true|undefined} comparator Comparator which is used in
+ * @param {function(actual, expected)|true|false} [comparator] Comparator which is used in
  *     determining if the expected value (from the filter expression) and actual value (from
  *     the object in the array) should be considered a match.
  *
@@ -54,13 +54,14 @@
  *   - `true`: A shorthand for `function(actual, expected) { return angular.equals(actual, expected)}`.
  *     This is essentially strict comparison of expected and actual.
  *
- *   - `false|undefined`: A short hand for a function which will look for a substring match in case
- *     insensitive way.
+ *   - `false`: A short hand for a function which will look for a substring match in a case
+ *     insensitive way. Primitive values are converted to strings. Objects are not compared against
+ *     primitives, unless they have a custom `toString` method (e.g. `Date` objects).
  *
- *     Primitive values are converted to strings. Objects are not compared against primitives,
- *     unless they have a custom `toString` method (e.g. `Date` objects).
  *
- * @param {string=} anyPropertyKey The special property name that matches against any property.
+ *   Defaults to `false`.
+ *
+ * @param {string} [anyPropertyKey] The special property name that matches against any property.
  *     By default `$`.
  *
  * @example