Merge branch 'stable-6.7' into stable-6.8

* stable-6.7:
  RefDirectory: Do not unlock until after deleting loose ref
  Add missing javadoc description for declared exception
  SnapshottingRefDirectory: Invalidate snapshot after locking ref for update
  SnapshottingRefDir: Replace lambas with method refs
  SnapshottingRefDir: Reduce casts with overrides
  [errorprone] Fix wrong comparison which always evaluated to false
  [errorprone] Remove unnecessary comparison

Change-Id: Ic6312bd3b2b1db38a287ebc7f31062251341438a

diff --cc org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/RefDirectory.java
Simple merge

diff --cc org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/SnapshottingRefDirectory.java
Simple merge