NullPointerException is caused by
com.ptc.core.meta.common.IllegalFormatException
at com.ptc.core.meta.common.impl.AbstractAssociationTypeIdentifier.newAssociationIdentifier(AbstractAssociationTypeIdentifier.java:566)
at com.ptc.core.meta.type.common.TypeInstanceHelper.acquireSingleAttributeIdentifier(TypeInstanceHelper.java:220)
at com.ptc.core.meta.type.common.TypeInstanceHelper.acquireNewAssociationIdentifier(TypeInstanceHelper.java:88)
at com.ptc.core.lwc.server.LWCNormalizedObject.set(LWCNormalizedObject.java:567)