RFR: 1909: Empty GET calls should be left empty

[Erik Joelsson]

Over the last week, we have had issues with JBS returning weird errors seemingly randomly, which has caused a lot of problems with the bots. It turns out our hosting provider has become more stringent with handling http/2 requests and no longer likes GET requests with a request body. Skara currently always fills in the body of a request, regardless of type, with an empty JSON document '{}' when the body is empty. This seems to be faulty behavior and we should let empty GET calls be empty instead.

I have been running staging with this patch over night and there were no errors.

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Commit messages:
 - Try forcing GET body to null

Changes: https://git.openjdk.org/skara/pull/1519/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1519&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1909
  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/skara/pull/1519.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1519/head:pull/1519

PR: https://git.openjdk.org/skara/pull/1519