_data produces an odd error if it receives an empty List
Summary: It's a transformation -- it should just allow empty lists through silently.
Eric reports:
The recipe as-given throws errors when there are no Conversations on a Thing (_data expects a value in its parameter, but it is empty) - it probably wants _isEmpty filtering. (Which I've added in my own use.)
That workaround works, but conceptually shouldn't be necessary: doing a transform on an empty List is entirely legal, and should simply produce the target type.
Have fixed this for _class / _data / _tooltip. But the bug is really in Invocation.processParamFirstGuts(), which produces an error if the result of processing is empty; it should only do so if the parameter is empty. Think about fixing this more generally.
