Empty Class-Path in JAR manifest attributes

Adding the Class-Path entry in JAR manifest no longer works.

I am not sure when it stopped working, as it has been a long time since I have started a java application directly with the JAR file.

Running Gradle 6.6.1 on Java 11/15
The configurations.runtime.collect now gives me an empty list.

What has happened, and how do I fix this?

My complete JAR Manifest in build.gradle:

jar {
    manifest {
            'Implementation-Title': project.name,
            'Implementation-Version': project.version,
            'Implementation-Vendor': vendorName,
            'Implementation-Vendor-Id': project.group,
            'Specification-Title': project.name,
            'Specification-Version': project.version,
            'Specification-Vendor': vendorName,
            'Automatic-Module-Name': 'com.company.app',
            'Application-Name': applicationName,
            'Main-Class': project.application.mainClass,
            'Class-Path': configurations.compile.collect { it.getName() }.join(' '),
            'Built-By': userName,
            'Build-Time': buildDateTime,
            'Created-By': createdBy,
            'Permissions': 'all-permissions',
            'Codebase': '*'