RFR: 7894: Provide an alternative Java based flamegraph visualization [v18]

[Brice Dutheil]

On Fri, 9 Jun 2023 15:31:11 GMT, Alex Macdonald <aptmac at openjdk.org> wrote:

>> That's really odd, could you share the JFR and the searched text
>
> Yeah sure, I'll send some info to you over slack

So it appears that a module can have no name.
I've used this search code in the past on various JFR files (in my "demo" fireplace application). I noticed the package name is `org.eclipse.osgi.framework.eventmgr`, I never tested with a recording of an OSGI app, so maybe there's something there causing the frame to create a "null" module.

![_null_ module](https://github.com/openjdk/jmc/assets/803621/9b358d47-a78c-404d-a17c-869c55ce9821)

Regardless the fix is simple.

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PR Review Comment: https://git.openjdk.org/jmc/pull/408#discussion_r1224506311