ListOf AMP Arguments should support 'optional' flag

[faldridge]

Like all other AMP Argument subclasses, t.p.amp.ListOf should allow callers to pass 'optional=True' to its init() method, thereby allowing the argument to be omitted from the protocol.

Attached is a patch that provides the correct behavior with the necessary update to ListOf's docstring.

As the functionality is handled by the base class (t.p.amp.Argument), and not individual subclasses, and as the functionality already has unit tests, there are no unit tests included in this patch.

[exarkun]

The patch looks good. Thanks. A couple things though:

1. In @foo docs, after the first line, lines should be indented 4 spaces.
2. The feature should have unit tests.

[faldridge]

Replying to exarkun:

The patch looks good. Thanks. A couple things though: 1. In @foo docs, after the first line, lines should be indented 4 spaces. 2. The feature should have unit tests.

1. Done. 2. Added.

[exarkun]

Thanks, looks good, I'll apply (including a news fragment).

[exarkun]

(In [29159]) Add optional parameter to twisted.protocols.amp.ListOf

Author: faldridge Reviewer: exarkun Fixes: #4474

Let ListOf arguments be optional in the usual way.