Generated javac wrapper crashes on bash < 4.4 (macOS ships 3.2): unguarded ${LAUNCHER_ARGS[@]} #987

Bug: the javac wrapper scip-java generates for Maven builds (via -Dmaven.compiler.executable=<tmp>/bin/javac) crashes under bash 3.2 — the only bash macOS ships by default.

Repro: any Maven-built Java project, scip-java index, on macOS with the default /bin/bash (3.2.57):

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.13.0:compile
  (default-compile): Fatal error compiling: Could not retrieve version from
  <tmp>/scip-java<N>/bin/javac. Exit code 1, Output:
  <tmp>/scip-java<N>/bin/javac: line 38: LAUNCHER_ARGS[@]: unbound variable

Root cause: the generated wrapper is:

#!/usr/bin/env bash
set -eu
...
LAUNCHER_ARGS=()
...
for arg in "$@"; do
  if [[ $arg == -J* ]]; then
    LAUNCHER_ARGS+=("$arg")
  fi
done
...
javac "${JAVAC_JVM_OPTIONS[@]}" "@$NEW_JAVAC_OPTS" "${LAUNCHER_ARGS[@]}"   # line 38

LAUNCHER_ARGS only ever collects -J* flags. maven-compiler-plugin's version probe (javac -version, used to validate the configured compiler executable before the real build) invokes the wrapper with no -J flags, so the array stays empty.

Under set -u, expanding an empty array ("${arr[@]}") is an error on bash < 4.4 — confirmed directly:

$ /bin/bash --version | head -1
GNU bash, version 3.2.57(1)-release (arm64-apple-darwin25)
$ /bin/bash -c 'set -eu; A=(); echo "${A[@]}"'
/bin/bash: A[@]: unbound variable

macOS has shipped only bash 3.2 as /bin/bash for over a decade (GPLv3 licensing), and does not include a newer bash by default. This means every Maven-built Java project fails to index on macOS unless the user happens to already have a newer bash earlier on PATH than /bin/bash — the wrapper's #!/usr/bin/env bash shebang resolves through PATH, so this is enough to work around it without patching scip-java, but it shouldn't be necessary.

Both JAVAC_JVM_OPTIONS and LAUNCHER_ARGS are exposed to this on line 38.

Suggested fix: bash-3.2-safe expansion, so the wrapper works regardless of which bash version is on PATH:

javac ${JAVAC_JVM_OPTIONS[@]+"${JAVAC_JVM_OPTIONS[@]}"} "@$NEW_JAVAC_OPTS" ${LAUNCHER_ARGS[@]+"${LAUNCHER_ARGS[@]}"}

(${arr[@]+"${arr[@]}"} expands to nothing when arr is unset/empty and to the normal quoted-expansion otherwise — safe on every bash version, no set -u interaction.)

Happy to send a PR with this one-line change if useful.