if you have
jboss-metadata-ear-11.0.0.Final.jar and jboss-metadata-common-11.0.0.Final.jar
on your module path, jvm complains as both jars export package org.jboss.metadata.merge
which violates the modules contract where only one module (jar) can provide single package.

example error that jvm prints

Error: Modules jboss.metadata.ear and jboss.metadata.common export package org.jboss.metadata.merge to module wildfly.clustering.common