RFR: 8209038: Clarify the javadoc of Cipher.getParameters() [v6]

[Valerie Peng]

> Anyone can help review this javadoc update? The main change is the wording for the method javadoc of Cipher.getParameters()/CipherSpi.engineGetParameters(). The original wording is somewhat restrictive and request is to broaden this to accommodate more scenarios such as when null can be returned.
> The rest are minor things like add {@code } to class name and null, and remove redundant ".". 
> 
> Will file CSR after the review is close to being wrapped up.
> Thanks~

Valerie Peng has updated the pull request incrementally with one additional commit since the last revision:

  Minor wording changes.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8117/files
  - new: https://git.openjdk.java.net/jdk/pull/8117/files/f9727edf..10228192

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8117&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8117&range=04-05

  Stats: 4 lines in 2 files changed: 0 ins; 2 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8117.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8117/head:pull/8117

PR: https://git.openjdk.java.net/jdk/pull/8117