FULL PRODUCT VERSION :
java version "10-ea"
Java(TM) SE Runtime Environment (build 10-ea+32)
Java HotSpot(TM) 64-Bit Server VM (build 10-ea+32, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 10.0.15063]

A DESCRIPTION OF THE PROBLEM :
When passing a unexpected character to the /env class-path command within the jshell, the jshell crashes

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
jshell> /env -class-path ?

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The same as in JDK 9:

jshell> /env class-path ?
| Unexpected arguments at end of command: [class-path, ?] -- class-path ?
ACTUAL -
The exception reported

ERROR MESSAGES/STACK TRACES THAT OCCUR :
jshell> /env -class-path ?
Exception in thread "main" java.nio.file.InvalidPathException: Illegal char <?> at index 0: ?
        at java.base/sun.nio.fs.WindowsPathParser.normalize(WindowsPathParser.java:182)
        at java.base/sun.nio.fs.WindowsPathParser.parse(WindowsPathParser.java:153)
        at java.base/sun.nio.fs.WindowsPathParser.parse(WindowsPathParser.java:77)
        at java.base/sun.nio.fs.WindowsPath.parse(WindowsPath.java:92)
        at java.base/sun.nio.fs.WindowsFileSystem.getPath(WindowsFileSystem.java:229)
        at java.base/java.nio.file.Paths.get(Paths.java:84)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool.toPathResolvingUserHome(JShellTool.java:1250)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool$OptionParserBase.lambda$validPaths$0(JShellTool.java:372)
        at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195)
        at java.base/java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:948)
        at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
        at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
        at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)
        at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
        at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:511)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool$OptionParserBase.lambda$validPaths$3(JShellTool.java:375)
        at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195)
        at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1492)
        at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
        at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
        at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)
        at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
        at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:511)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool$OptionParserBase.validPaths(JShellTool.java:379)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool$OptionParserBase.parse(JShellTool.java:414)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool$OptionParserBase.parse(JShellTool.java:350)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool.parseCommandLineLikeFlags(JShellTool.java:2873)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool.cmdEnv(JShellTool.java:2841)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool.lambda$new$42(JShellTool.java:1650)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool.processCommand(JShellTool.java:1221)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool.run(JShellTool.java:1147)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool.start(JShellTool.java:919)
        at jdk.jshell/jdk.internal.jshell.tool.JShellToolBuilder.run(JShellToolBuilder.java:239)
        at jdk.jshell/jdk.internal.jshell.tool.JShellToolProvider.main(JShellToolProvider.java:119)

REPRODUCIBILITY :
This bug can be reproduced always.