NPE When ObjectClass Attribute Missing

In the code below the attribute is not added to the attributes. When attempting to create a subcontext, this results in an NPE.

========================================
Attributes attributes =
new BasicAttributes();
Attribute attribute =
new BasicAttribute(
"objectClass",
"top");
attribute.add("subentry");
directoryContextL0 =
(DirContext)
testPartitionContext.
createSubcontext(l0RDN, attributes);

directoryContextL1 =
(DirContext)
directoryContextL0.
createSubcontext(l1RDN, attributes);
========================================

When I try running the test above I get this:

org.apache.directory.server.core.interceptor.InterceptorException: Unexpected exception. [Root exception is java.lang.NullPointerException]