There is a typo in in the linux/MacOS launcher visualvm/launcher/visualvm

On line 135, it reads:

if [ ! -z "$visualvm_extraclusters" ] ; then
    visualvm_clusters ="$visualvm_clusters:$visualvm_extraclusters"
fi

The extra space before the "=" on line 135, breaks the script ("command not found" error) and prevents therefore the loading of extra modules which is annoying during development of a new module for VisualVM.

It shall read:

if [ ! -z "$visualvm_extraclusters" ] ; then
    visualvm_clusters="$visualvm_clusters:$visualvm_extraclusters"
fi