RFR: 8357597: Proxy.getInvocationHandler throws NullPointerException instead of IllegalArgumentException for null

[Steffen Nießing]

`Proxy#getInvocationHandler(Object)` throws a `NullPointerException` if the specified argument is `null`. This PR adds the missing `throws` declaration for the NPE.

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Commit messages:
 - 8357597: Add throws declaration for NPE

Changes: https://git.openjdk.org/jdk/pull/25419/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25419&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357597
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/25419.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25419/head:pull/25419

PR: https://git.openjdk.org/jdk/pull/25419