No check if the Base Directory Path is filled when enable HUD is checked. Leading to HUD not starting

[globeone]

Describe the bug
On the Weekly version of ZAP the HUD hasn't loaded in the browser for the last 4 or so weeks of versions. The HUD is enabled.

To Reproduce
Steps to reproduce the behavior:

1. Go to Manual Explore
   1a. Enter a url "https://example.org"
2. Click on enable HUD
3. Scroll down to Chrome or Firefox
   3a. Click on Launch Browser
4. See no HUD

Expected behavior
When launching the HUD, the HUD should show up in the browser

Screenshots

Software versions

• ZAP: D-2020-10-26

• Add-on:
  D2020-10-26_InstalledPlugins.xlsx

• OS: Windows 10

• Java: Bellsoft Liberica JDK 15

• Browser:
  Chrome: Version 86.0.4240.111 (Official Build) (64-bit)
  Firefox: 82.0.2 (64-bit)

Errors from the zap.log file
D2020-10-26_ZAPHUD_injectionhtmlNotFound.txt

Additional context
In the log file we see that the relative path to injectionHtml.html is incorrect. Java then defaults to a absolute path of No such file C:\target\injectionHtml.html that doesn't exist.
the absolute path being (for the weekly version)
C:\Users$USER\OWASP ZAP_D\hud\target\

Would you like to help fix this issue?
Happy to test and report bugs.

[psiinon]

Strictly speaking this looks like a local config issue, but no problem with trying to fix invalid or missing paths.

[globeone]

So, there is no check if the Base Directory is blank in the options.

It would be desirable to have a check if the Base Directory field is filled when the 'enable HUD' option is checked to prevent this issue from occurring in the future.

[psiinon]

Agreed :)