RFR: 8224158: assertion related to NPE at DynamicCallSiteDesc::withArgs should be reworded

[Vicente Romero]

This is a very small patch that is just rewording the spec for DynamicCallSiteDesc::withArgs. Basically adding that NPE can also be thrown if the content of the argument is `null`

TIA for the review

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Commit messages:
 - 8224158: assertion related to NPE at DynamicCallSiteDesc::withArgs should be reworded

Changes: https://git.openjdk.java.net/jdk/pull/4067/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4067&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8224158
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4067.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4067/head:pull/4067

PR: https://git.openjdk.java.net/jdk/pull/4067