JDK-8325262 improves the error message to print the exception message of FindException without the stack trace. This can further be improved to show the cause message that will help the users to diagnose the invalid JAR input file.

$ jdeps --ignore-missing-deps --jdk-internals test.jar
Exception in thread "main" java.lang.module.FindException: Error reading module: test.jar
    at java.base/jdk.internal.module.ModulePath.readModule(ModulePath.java:350)
    at java.base/jdk.internal.module.ModulePath.scan(ModulePath.java:237)
    at java.base/jdk.internal.module.ModulePath.scanNextEntry(ModulePath.java:190)
    at java.base/jdk.internal.module.ModulePath.findAll(ModulePath.java:166)
    at jdk.jdeps/com.sun.tools.jdeps.JdepsConfiguration$Builder.build(JdepsConfiguration.java:521)
    at jdk.jdeps/com.sun.tools.jdeps.JdepsTask.buildConfig(JdepsTask.java:603)
    at jdk.jdeps/com.sun.tools.jdeps.JdepsTask.run(JdepsTask.java:557)
    at jdk.jdeps/com.sun.tools.jdeps.JdepsTask.run(JdepsTask.java:533)
    at jdk.jdeps/com.sun.tools.jdeps.Main.main(Main.java:49)
Caused by: java.lang.module.InvalidModuleDescriptorException: DeprecatedAuthExtensionsPlaceholder.class found in top-level directory (unnamed package not allowed in module)
    at java.base/jdk.internal.module.ModulePath.toPackageName(ModulePath.java:720)
    at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:197)
    at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:197)
    at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:179)
    at java.base/java.util.zip.ZipFile$EntrySpliterator.tryAdvance(ZipFile.java:558)
    at java.base/java.util.Spliterator.forEachRemaining(Spliterator.java:332)
    at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509)
    at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
    at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:921)
    at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
    at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:682)
    at java.base/jdk.internal.module.ModulePath.jarPackages(ModulePath.java:621)
    at java.base/jdk.internal.module.ModulePath.lambda$readJar$6(ModulePath.java:653)
    at java.base/jdk.internal.module.ModuleInfo.doRead(ModuleInfo.java:311)
    at java.base/jdk.internal.module.ModuleInfo.read(ModuleInfo.java:129)
    at java.base/jdk.internal.module.ModulePath.readJar(ModulePath.java:652)
    at java.base/jdk.internal.module.ModulePath.readModule(ModulePath.java:331)
    ... 8 more