RFR: 8358159: empty mode/padding in cipher transformations.

[Varada M]

Omitting the mode/padding in a transformation string eg: "AES/ /NoPadding" throws NoSuchAlgorithmException.
This patch restores the behavior by ensuring that empty mode or padding strings are interpreted as null.

Testing done for : tier1 - fastdebug level

JBS: [JDK-8358159](https://bugs.openjdk.org/browse/JDK-8358159)

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Commit messages:
 - JDK-8358159: empty mode/padding in cipher transformations.

Changes: https://git.openjdk.org/jdk/pull/25547/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25547&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8358159
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/25547.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25547/head:pull/25547

PR: https://git.openjdk.org/jdk/pull/25547