Board Manager Update results in java.lang.NullPointerException

[bdlabitt]

IDE 1.8.13, Platform linux64, Ubuntu 20.04.1
Have not be able to update boards using board manager. This error is the same as reported #10335 (and closed) last year. The apparent solution does not appear to be robust, since it has reoccured. I cannot update the Arduino SAMD board support package. Currently at 1.8.9. Clicking update results in the error.

java.lang.NullPointerException
java.lang.RuntimeException: java.lang.NullPointerException
	at cc.arduino.contributions.packages.ui.ContributionManagerUI.lambda$onInstallPressed$2(ContributionManagerUI.java:175)
	at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NullPointerException
	at cc.arduino.contributions.packages.ContributionInstaller.remove(ContributionInstaller.java:276)
	at cc.arduino.contributions.packages.ui.ContributionManagerUI.lambda$onInstallPressed$2(ContributionManagerUI.java:170)
	... 1 more

Is the solution still to delete .arduino15/cache/cache.json and ./arduino15/package_index.json and restart the Arduino IDE, as stated by facchinm on June 10, 2020?

[bdlabitt]

No, to answer my question, this fix does not work. Renaming the above files, does not fix the error.

[matthijskooijman]

I think this is a completely different problem. The NullPointerException error is just a generic indication that some variable is null when it shouldn't be, and looking at the backtrace, the cause is completely different.

Looking at the backtrace, the exception is caused here:

Arduino/arduino-core/src/cc/arduino/contributions/packages/ContributionInstaller.java

Lines 275 to 276 in 5adf408

	log.info("The directory is not empty there is another version installed. directory {}",
	destFolder.getParentFile().toPath(), e);

Called from here:

Arduino/app/src/cc/arduino/contributions/packages/ui/ContributionManagerUI.java

Line 170 in 5adf408

errors.addAll(installer.remove(platformToRemove));

So it seems it's either destFolder that is null, or destFolder.getParentFile() is null (I think getParentFile() can return null when destFolder is already the root path / or maybe an empty path).

I haven't dug further, so I have no advice on what could cause this or how to work around this, but hopefully the above helps others to figure out what's going on...