Maven build on a new machine fails without private key

[raner]

[INFO] --- maven-gpg-plugin:1.6:sign (sign-artifacts) @ projo-parent ---
gpg: directory '/Users/mirko/.gnupg' created
gpg: keybox '/Users/mirko/.gnupg/pubring.kbx' created
gpg: no default secret key: No secret key
gpg: signing failed: No secret key
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary for Projo Parent POM 1.2.0-SNAPSHOT:
[INFO] 
[INFO] Projo Parent POM ................................... FAILURE [  1.303 s]
[INFO] Projo Template Annotations ......................... SKIPPED
[INFO] Projo Template Configuration ....................... SKIPPED
[INFO] Projo Template Generation .......................... SKIPPED
[INFO] Projo .............................................. SKIPPED
[INFO] Projo Runtime Code Generation ...................... SKIPPED
[INFO] Projo Jackson Integration .......................... SKIPPED
[INFO] Projo JAX-RS Integration for Jersey ................ SKIPPED
[INFO] Projo Template Generation Tests .................... SKIPPED
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  1.731 s
[INFO] Finished at: 2020-07-22T16:41:39-07:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-gpg-plugin:1.6:sign (sign-artifacts) on project projo-parent: Exit code: 2 -> [Help 1]

This is almost certainly a Maven misconfiguration; for a regular non-release build no PGP key should be necessary.