Gradle MavenPublication: "Task has not declared any outputs despite executing actions" - maven

Question

I want to publish a zip archive to a remote maven repository. The task zipSources packs a sample file into a zip archive. The publication myPubliction publishes to mavenLocal and to the remote maven repository.
The publication works - I can see the packages uploaded to the remote repository. But the build still fails with
> Task :publishMyPublicationPublicationToMavenRepository FAILED
Task ':publishMyPublicationPublicationToMavenRepository' is not up-to-date because:
Task has not declared any outputs despite executing actions.
Publishing to repository 'maven' (null)
FAILURE: Build failed with an exception.
What am I missing? How do I declare outputs for the publishing action? Or is there another cause?
Here is my build.gradle:
plugins {
id "maven-publish"
}
group = 'com.example.test'
version = '0.0.1-SNAPSHOT'
task zipSources(type: Zip, group: "Archive", description: "Archives source in a zip file") {
from ("src") {
include "myfile.txt"
}
into "dest"
baseName = "helloworld-demo"
destinationDir = file("zips")
}
publishing {
publications {
myPublication(MavenPublication) {
artifactId = 'my-library'
artifact zipSources
pom {
name = 'My Library'
description = 'A concise description of my library'
}
}
}
repositories {
maven {
mavenLocal()
}
maven {
url "http://nexus.local/content/repositories/snapshots"
credentials {
username = 'admin'
password = 'admin'
}
}
}
}

Answer 1

It appears there must not be a mavenLocal() declaration inside repositories, as per https://docs.gradle.org/current/userguide/publishing_maven.html#publishing_maven:install