Throw sensible exception in case of deserialization error or output warning

[msiebert-dev]

When creating a v3.0 aasx file with Package Explorer the output xml may contain self closing tags as is the case in the following snippet:
<semanticId> <type>ExternalReference</type> <keys /> </semanticId>

The empty <keys /> tag leads to deserialization failure in the XMLDeserialzer read method.
The same applies for self closing <outputVariables/> , <inoutputVariables /> or <multiLanguageProperty><value /></multiLanguageProperty> tags.
A check for null may be sufficient as in the EmbeddedDataSpecificationsDeserializer deserialize method. A self cosing <embeddedDataSpecifications /> tag doesn't lead to deserialization failure.

If the self closing <!-- keys /--> tag is commented out the deserialization doesn't fail, although the reference is invalid according to the specification because it doesn't contain any <key>.

A sensible exception or a warning would be helpful.

Attached is a v2.0 zip file which after renaming to .aasx and saving in Package Explorer lead to a deserialization failure when read with AASXDeserializer.java.
DrillerInstance - Instance.zip

[msiebert-dev]

If the <!-- keys /--> tag is commented out the deserialization doesn't fail any more. According to the specification however a reference without a <key> is not valid.

[FrankSchnicke]

Please see #172.
To summarize, this is an issue with the AASX Package Explorer not creating spec conforming AASX files. Feel free to create an issue in the AASX Package Explorer repository.

[alexgordtop]

@FrankSchnicke You are right and we already did this:
https://github.com/admin-shell-io/temp-aasx-package-explorer/issues/97

But shouldn't the import / reader race at least a warning, that there are invalid SemanticIds included in the imported aasx?
As @msiebert-dev wrote, if keys are not present, then the importer would import an invalid reference...
...only with type, but without keys.

Or should we afterwards execute an explicit validation?