Fuseki/TDB: BadURIException in DatasetAccessor.putModel

I'm attempting to write a new graph into my TDB repository. The graph has the name of the instance it represents, in this case, "http://anchor/plan#Graph1".

Deep below DatasetAccessor.putModel(), I get the following error:

com.hp.hpl.jena.shared.BadURIException: Only well-formed absolute URIrefs can be included in RDF/XML output: <> Code: 57/REQUIRED_COMPONENT_MISSING in SCHEME: A component that is required by the scheme is missing.

Placing a breakpoint where the exception is thrown reveals that BaseXMLWrite.checkURI has been given an empty String.

So, I looked for empty URI strings in the Model being written, at least as represented in Eclipse's toString() output. I'm not sure what format(s) the following is in, but I see empty subjects in some triples, all of which are associated with the ontology imports. (It has been edited to remove proprietary info):

<ModelCom
{ @owl:imports http://www.w3.org/2003/01/geo/wgs84_pos;
@owl:imports http://anchor/OntS;
@owl:imports http://anchor/OntC;
@owl:imports http://anchor/OntA;
@owl:imports http://anchor/Core;
@rdf:type owl:Ontology;
http://anchor/plan#Graph1 @cc:meta_modifiedTime "2014-04-21T15:23:40.427Z"^^http://www.w3.org/2001/XMLSchema#dateTime;
http://anchor/plan#Graph1 @cc:meta_createdTime "2014-04-21T15:23:40.427Z"^^http://www.w3.org/2001/XMLSchema#dateTime;
.....
http://anchor/plan#Graph1 @rdf:type OntS:SObject} |
[, http://www.w3.org/2002/07/owl#imports, http://www.w3.org/2003/01/geo/wgs84_pos]
[, http://www.w3.org/2002/07/owl#imports, http://anchor/OntS]
[, http://www.w3.org/2002/07/owl#imports, http://anchor/OntC]
[, http://www.w3.org/2002/07/owl#imports, http://anchor/OntA]
[, http://www.w3.org/2002/07/owl#imports, http://anchor/Core]
[, http://www.w3.org/1999/02/22-rdf-syntax-ns#type, http://www.w3.org/2002/07/owl#Ontology]
[http://anchor/plan#Graph1, http://anchor/Core#meta_modifiedTime, "2014-04-21T15:23:40.427Z"^^http://www.w3.org/2001/XMLSchema#dateTime]
[http://anchor/plan#Graph1, http://anchor/Core#meta_createdTime, "2014-04-21T15:23:40.427Z"^^http://www.w3.org/2001/XMLSchema#dateTime]
.....
[http://anchor/plan#Graph1, http://www.w3.org/1999/02/22-rdf-syntax-ns#type, http://anchor/OntS#SObject]>

Any ideas?

Dave Lebling