Improve exception message when BundlesAction.createBundleArtifactKey(...) fails with the below stack trace, to at least know which .jar file couldn't be read.
[ERROR] Could not resolve content of rcp.target
[ERROR] org.eclipse.core.runtime.AssertionFailedException: null argument:
[ERROR] at org.eclipse.core.runtime.Assert.isNotNull(Assert.java:88)
[ERROR] at org.eclipse.core.runtime.Assert.isNotNull(Assert.java:76)
[ERROR] at org.eclipse.equinox.internal.p2.metadata.ArtifactKey.<init>(ArtifactKey.java:79)
[ERROR] at org.eclipse.equinox.p2.publisher.eclipse.BundlesAction.createBundleArtifactKey(BundlesAction.java:134)
[ERROR] at org.eclipse.tycho.p2.resolver.FileTargetDefinitionContent.readBundles(FileTargetDefinitionContent.java:167)
[ERROR] at org.eclipse.tycho.p2.resolver.FileTargetDefinitionContent.preload(FileTargetDefinitionContent.java:89)
[ERROR] at org.eclipse.tycho.p2.resolver.FileTargetDefinitionContent.query(FileTargetDefinitionContent.java:73)
[ERROR] at org.eclipse.tycho.p2.target.TargetDefinitionResolver.resolveContentWithExceptions(TargetDefinitionResolver.java:170)
[ERROR] at org.eclipse.tycho.p2.target.TargetDefinitionResolver.resolveContent(TargetDefinitionResolver.java:110)
[ERROR] at org.eclipse.tycho.p2.target.TargetDefinitionResolverService.resolveFromArguments(TargetDefinitionResolverService.java:86)
[ERROR] at java.base/java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1708)
[ERROR] at org.eclipse.tycho.p2.target.TargetDefinitionResolverService.getTargetDefinitionContent(TargetDefinitionResolverService.java:59)
[ERROR] at org.eclipse.tycho.p2.target.TargetPlatformFactoryImpl.resolveTargetDefinitions(TargetPlatformFactoryImpl.java:209)
[ERROR] at org.eclipse.tycho.p2.target.TargetPlatformFactoryImpl.createTargetPlatform(TargetPlatformFactoryImpl.java:161)
[ERROR] at org.eclipse.tycho.p2.target.TargetPlatformFactoryImpl.createTargetPlatform(TargetPlatformFactoryImpl.java:134)
[ERROR] at org.eclipse.tycho.p2.resolver.P2ResolverImpl.resolveMetadata(P2ResolverImpl.java:174)
[ERROR] at org.eclipse.tycho.extras.tpvalidator.TPValidationMojo.validateTarget(TPValidationMojo.java:223)
[ERROR] at org.eclipse.tycho.extras.tpvalidator.TPValidationMojo.execute(TPValidationMojo.java:152)
[ERROR] at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:126)
(cherry picked from commit af2b6be)