RFR: 8231107: Allow store password to be null when saving a PKCS12 KeyStore

[Weijun Wang]

You can create a password-less PKCS12 KeyStore file now by calling `ks.store(outStream, null)` no matter what the default cert protection algorithm and Mac algorithm are defined in `java.security`.

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Commit messages:
 - 8231107: Storing PKCS12 keystore without integrity protection and no enc certs not easy

Changes: https://git.openjdk.java.net/jdk/pull/5950/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5950&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8231107
  Stats: 59 lines in 2 files changed: 29 ins; 16 del; 14 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5950.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5950/head:pull/5950

PR: https://git.openjdk.java.net/jdk/pull/5950