* Unit tests were wrong given the annotation for test_array_int_null_in and
  test_array_int_null_out:

  /**
   * test_array_int_null_in:
   * @arr: (array length=len) (allow-none):
   * @len: length
   */

 -- and --

  /**
   * test_array_int_null_out:
   * @arr: (out) (array length=len) (allow-none):
   * @len: (out) : length
   */

  The (array length=len) annotation meant we don't pass in or
  receive the len argument as this is handled under the hood
  (Python's representation of an array, the list type, encapsulates
   the length inside the type)

* Fixing up the tests revealed a latent crasher bug when passing None to an
  interface that accepts an array.  The fix was to check for NULL and set
  the length argument to 0 when invoking the bound method.

https://bugzilla.gnome.org/show_bug.cgi?id=619235