code: public static int findIndexOf(Object self, int startIndex, Closure condition) {
          return findIndexOf(InvokerHelper.asIterator(self), condition);
      }
docs: Iterates over the elements of an aggregate of items, starting from a
  specified startIndex, and returns the index of the first item that matches the
  condition specified in the closure.
  
  @param self       the iteration object over which to iterate
  @param startIndex start matching from this index
  @param condition  the matching condition
  @return an integer that is the index of the first matched object or -1 if no match was found
  @since 1.5.0