RFR: 8277932: Subject:callAs() not throwing NPE when action is null

[Weijun Wang]

Add null check. I must have thought the NPE will be thrown anyway but the `catch Exception` block swallows it.

I added a noreg-trivial label. If you think differently can add one.

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Commit messages:
 - 8277932: Subject:callAs() not throwing NPE when action is null

Changes: https://git.openjdk.java.net/jdk/pull/6728/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6728&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8277932
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6728.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6728/head:pull/6728

PR: https://git.openjdk.java.net/jdk/pull/6728