[R-Source] Improve R AST
  - Change RAstNode.getOperator to non-null if possible
  - Change RAstNode.getText to null for missing nodes
  - Improve unit tests

Change-Id: I67fce41df1efb423a1ba1748ceb0b5549a0235d8
12 files changed
tree: 68aa657223bc5d494768e162ff5ae8a15174c905
  1. .settings/
  2. r/
  3. redocs/
  4. rhelp/
  5. rtm/
  6. .project
  7. LICENSE
  8. NOTICE.md
  9. pom.xml