GC_TUNE setting from solr.in.sh is not applied

[Steffen Moldenhauer]

Hi all,

I installed Solr 8.4.1 (first time on a linux sub-system for testing purposes 
only) and for whatever reason the default GC settings prevented the server from 
running.
So I tried to change the setting with a GC_TUNE in solr.in.sh

But it got not applied to the start up. So I looked at the /solr-8.4.1/bin/solr 
Script and found:

  if [ -z ${GC_TUNE+x} ]; then
      GC_TUNE=('-XX:+UseG1GC' \

${GC_TUNE+x} looks strange to me - but I do not really know that much about 
shell-programming

Changed it to
if [ -z "$GC_TUNE" ]; then

and my setting from solr.in.sh got applied.

There's also: SOLR_JAVA_STACK_SIZE+x GC_LOG_OPTS+x Is that kind of syntax 
really working or is it wrong?

Regards
Steffen