[code-reflection] Integrated: Adding empty string to java's ProcessBuilder seeems problematic

[Gary Frost]

Weird bug. 

Seems like adding an empty "" string to List<String> then 'joining' this list to create opts for a ProcessBuilder seems to stop the ProcessBuilder from adding all opts/args. 

This fixes hat.java

-------------

Commit messages:
 - Adding empty string to java's ProcessBuilder seeems problematic

Changes: https://git.openjdk.org/babylon/pull/705/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=705&range=00
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/babylon/pull/705.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/705/head:pull/705

PR: https://git.openjdk.org/babylon/pull/705