With weaving enabled, updates on an element collection of embeddables can potentially throw a null pointer exception.
For more information, see EclipseLink Issue report.
Two workarounds are available:
Add the annotation @ChangeTracking(DEFFERED) on the embeddable and set the property eclipselink.weaving.internal to false, or
Set the following properties to false in persistence XML: eclipselink.weaving.changetracking and eclipselink.weaving.internal.