The man page for "jar" contains:

Create jar file
    jar c[v0Mmfe] [manifest] [jarfile] [entrypoint] [-C dir] inputfiles [-Joption]

Update jar file
    jar u[v0Mfe] [manifest] [jarfile] [entrypoint] [-C dir] inputfiles [-Joption]

The command line for "update" is inexplicably missing the "m" flag, even though
the "manifest" argument is there. Probably we need to simply change
v0Mfe to v0Mmfe as in "create".