Validator crashes when sample rate not set and response is empty

[nackerley]

According to the StationXML specification, the sample rate is optional, and the response has no required attribues, so it can be empty: https://docs.fdsn.org/projects/stationxml/en/latest/reference.html#samplerate

Others have noted the importance of being able to leave sample rate unspecified for pre-digital channels which nonetheless have coordinates and can associated network-station-location-channel codes, see #144.

When I attempt to validate StationXML without sample rate but with an empty response, e.g. CN_subset.xml, the validator crashes:

(.venv) [nackerle@pc-nackerle test]$ java -jar $bin/stationxml-validator-1.7.5.jar --input CN_subset.xml
[2025-12-02 17:16:52] [SEVERE] edu.iris.dmc.Application exitWithError: edu.iris.dmc.station.conditions.SampleRateCondition.evaluate(SampleRateCondition.java:41)
edu.iris.dmc.station.rules.Rule.execute(Rule.java:44)
edu.iris.dmc.station.RuleEngineService.executeAllRules(RuleEngineService.java:160)
edu.iris.dmc.station.RuleEngineService.executeAllRules(RuleEngineService.java:142)
edu.iris.dmc.station.RuleEngineService.executeAllRules(RuleEngineService.java:108)
edu.iris.dmc.station.RuleEngineService.executeAllRules(RuleEngineService.java:47)
edu.iris.dmc.Application.run(Application.java:183)
edu.iris.dmc.Application.run(Application.java:168)
edu.iris.dmc.Application.run(Application.java:147)
edu.iris.dmc.Application.main(Application.java:118)

It turns out that if I delete the empty <Response/> tag, validation completes successfully. This empty tag is being produced by the SeisComP FDSNWS - it was not in the original FDSN StationXML converted to SeisComP XML to construct the inventory in SeisComP - so I can't get rid of it easily, but it's not invalid. I can also get validation to complete successfully if I add a dummy sample rate and remove both the empty response tag and the datalogger specification.