RFR: 8263565: NPE was thrown when sun.jvm.hotspot.rmi.serverNamePrefix was set

[Yasumasa Suenaga]

NPE was thrown when I set server name prefix for debugd as following:

$ jhsdb -J-Dsun.jvm.hotspot.rmi.serverNamePrefix=test debugd --pid 781
Attaching to process ID 781 and starting RMI services, please wait...
Error attaching to process or starting server: sun.jvm.hotspot.debugger.DebuggerException: java.lang.NullPointerException: Cannot invoke "String.length()" because "this.input" is null
        at jdk.hotspot.agent/sun.jvm.hotspot.RMIHelper.rebind(RMIHelper.java:78)
        at jdk.hotspot.agent/sun.jvm.hotspot.HotSpotAgent.setupDebugger(HotSpotAgent.java:379)
        at jdk.hotspot.agent/sun.jvm.hotspot.HotSpotAgent.go(HotSpotAgent.java:329)
        at jdk.hotspot.agent/sun.jvm.hotspot.HotSpotAgent.startServer(HotSpotAgent.java:215)
        at jdk.hotspot.agent/sun.jvm.hotspot.SALauncher.runDEBUGD(SALauncher.java:431)
        at jdk.hotspot.agent/sun.jvm.hotspot.SALauncher.main(SALauncher.java:493)
Caused by: java.lang.NullPointerException: Cannot invoke "String.length()" because "this.input" is null
        at java.base/java.net.URI$Parser.parse(URI.java:3166)
        at java.base/java.net.URI.<init>(URI.java:623)
        at java.rmi/java.rmi.Naming.intParseURL(Naming.java:273)
        at java.rmi/java.rmi.Naming.parseURL(Naming.java:237)
        at java.rmi/java.rmi.Naming.rebind(Naming.java:171)
        at jdk.hotspot.agent/sun.jvm.hotspot.RMIHelper.rebind(RMIHelper.java:64)
        ... 5 more

`serverNamePrefix` would not affect due to trivial bug.

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Commit messages:
 - 8263565: NPE was thrown when sun.jvm.hotspot.rmi.serverNamePrefix was set

Changes: https://git.openjdk.java.net/jdk/pull/3000/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3000&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8263565
  Stats: 3 lines in 1 file changed: 0 ins; 1 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3000.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3000/head:pull/3000

PR: https://git.openjdk.java.net/jdk/pull/3000