[CommonMark] Improve code of core-tests

  - Add more nullable annotations
  - Add missing generic parameters
  - Make use of Java 11 API

Change-Id: Id8d35b5cadfeba50b9e47b3cb7b1c05c307bf5c7
39 files changed
tree: 95c53421ce0ba857219d7964e5a7b32f610f821d
  1. .settings/
  2. docmlet/
  3. yaml/
  4. .project
  5. LICENSE
  6. NOTICE.md
  7. pom.xml