RFR: 8304445: Remaining uses of NULL in ciInstanceKlass.cpp

[Ilya Korennoy]

8304445: Remaining uses of NULL in ciInstanceKlass.cpp

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Commit messages:
 - 8304445: Replace remaining uses of NULL in ciInstanceKlass.cpp

Changes: https://git.openjdk.org/jdk/pull/13178/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13178&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304445
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/13178.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13178/head:pull/13178

PR: https://git.openjdk.org/jdk/pull/13178