When adding an Ivy resolver, forgetting to set its name causes an exception. So

dependencies {
    classpathResolvers.add(new URLResolver()) {
        // no name = "..." here

        addIvyPattern("...")
        addArtifactPattern("...")
    }
}

fails when trying to resolve dependencies when either Gradle or Ivy, I'm not sure, tries to put the resolver into a hash table (probably with its name as the key).

A message that says that a resolver needs a name would be much more user-friendly, of course.