java.lang.NullPointerException in Boards Manager updating "Arduino SAMD Boards (32-bits ARM Cortex-M0+)"

When using Boards Manager, the "**Arduino SAMD Boards (32-bits ARM Cortex-M0+)**" definition shows up as Updatable, but when I click on "Update" I get an error message:

**java.lang.NullPointerException**

in the console I see:

**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**

Because of this error I am unable to update the definitions for the affected boards.

Reproduce the Boards Manager update for Arduino SAMD Boards (32-bits ARM Cortex-M0+) and start with the stack trace locations in ContributionManagerUI.java and ContributionInstaller.java, especially lines 170, 175, and 276. Done means the affected board definition updates successfully without the reported NullPointerException.

Written by the indexing model from the issue text.