Currently jcmd command GC.heap_dump only works with an additionally provided file name.
Syntax : GC.heap_dump [options] <filename>

In case the JVM has the XX-flag HeapDumpPath set, we should support an additional mode where the <filename> is optional.
In case the filename is NOT set, we take the HeapDumpPath (file or directory).

new syntax :
GC.heap_dump [options] <filename> ... has precedence over second option
GC.heap_dump [options] … in case -XX:HeapDumpPath=p is set

This would be a simplification e.g. for support cases where a filename or directory is set at JVM startup with -XX:HeapDumpPath=p and writing to the path is intended/recommended for usage also in the jcmd case.