code: @Nonnull
    public static FieldValue arrayRemove(@Nonnull Object... elements) {
      Preconditions.checkArgument(elements.length > 0, "arrayRemove() expects at least 1 element");
      return new ArrayRemoveFieldValue(Arrays.asList(elements));
    }
docs: Returns a special value that can be used with set(), create() or update() that tells the server
  to remove the given elements from any array value that already exists on the server. All
  instances of each element specified will be removed from the array. If the field being modified
  is not already an array it will be overwritten with an empty array.
  
  @param elements The elements to remove from the array.
  @return The FieldValue sentinel for use in a call to set() or update().