JsonPath transformation service comply with the contract

[sjsf]

...as it was returning null in case the path pointed to an element which did not exist.
Now it throws a TransformationException.

I'm not 100% sure though if this really is always the right way of fixing it. A missing element in JSON is somewhat similar to "intentionally null", i.e. UndefType.UNDEF might also be a consideration. Any deeper insights anybody?

fixes #4376
Signed-off-by: Simon Kaufmann simon.kfm@googlemail.com

[kaikreuzer]

Any deeper insights anybody?

Not from my end.
Shall we wait for insights from others or "just merge"...?

[sjsf]

Then suggest using merging it because it now fits to the javadoc contract. If it turns out this is not appropriate, then we still can adapt it afterwards.

[martinvw]

Hmm, reading your suggestion UndefType.UNDEF or UndefType.NULL might make more sense, it is after all an element which may be only missing this time. And it's not uncommon in JSON the leave out any null values, see for example some NPE's I got in the Nest binding because I do not posses all Nest devices.

[htreu]

lgtm, should be merged.

[htreu]

@martinvw imho the transformation service is right about throwing a TransformationException. Its in the responsibility of the caller to act appropriate. And from the code I saw the exception is handled well by all callers.