How to configure Fuseki to work with several graphs as a joint dataset?

[Svensson, Lars]

Greetings,

I have several TDB2 datasets that I want to expose as named graphs and as a 
joint dataset. My basic idea is to have each TDB2 dataset as its own graph and 
then a joint dataset combining all graphs with the default graph being the 
union of all named graphs. My configuration is:

@prefix fuseki:  <http://jena.apache.org/fuseki#> .
@prefix rdf:     <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs:    <http://www.w3.org/2000/01/rdf-schema#> .
@prefix tdb2:     <http://jena.hpl.hp.com/2016/tdb#> .
@prefix ja:      <http://jena.hpl.hp.com/2005/11/Assembler#> .
@prefix :        <#> .

<#service1> rdf:type fuseki:Service ;
    fuseki:name                     "/dnb" ;   # http://host:port/dnb
    fuseki:serviceQuery             "query" ;    # SPARQL query service
    fuseki:serviceReadGraphStore    "data" ;     # SPARQL Graph store protocol 
(read only)
    fuseki:dataset           <#dnb> ;
    .

<#dnb> a ja:RDFDataset ;
    tdb2:unionDefaultGraph true ;
    ja:namedGraph [
        ja:graphName <https://d-nb.info/datasets/authorities#dataset> ;
        ja:graph <#authorities>
    ];
    ja:namedGraph [
        ja:graphName <https://d-nb.info/datasets/bib#dataset> ;
        ja:graph <#bib>
    ];
    ja:namedGraph [
        ja:graphName <https://d-nb.info/datasets/dnb-all#dataset> ;
        ja:graph <#dnb-all>
    ];
    ja:namedGraph [
        ja:graphName <https://d-nb.info/datasets/zdb#dataset> ;
        ja:graph <#zdb>
    ];
    .
<#authorities> a tdb2:GraphTDB ;
    tdb2:dataset <#dataset-authorities> .
<#bib> a tdb2:GraphTDB ;
    tdb2:dataset <#dataset-bib> .
<#dnb-all> a tdb2:GraphTDB ;
    tdb2:dataset <#dataset-dnb-all> .
<#zdb> a tdb2:GraphTDB ;
    tdb2:dataset <#dataset-zdb> .

<#dataset-authorites> a tdb2:DatasetTDB ;
    tdb2:location "/home/svensson/fuseki-data/dnb/authorities/" .
<#dataset-bib> a tdb2:DatasetTDB ;
    tdb2:location "/home/svensson/fuseki-data/dnb/bib/" .
<#dataset-dnb-all> a tdb2:DatasetTDB ;
    tdb2:location "/home/svensson/fuseki-data/dnb/dnb-all/" .
<#dataset-zdb> a tdb2:DatasetTDB ;
    tdb2:location "/home/svensson/fuseki-data/dnb/zdb/" .

When I start Fuseki, I get the following error message:

[2019-01-15 11:14:13] Server     ERROR Exception in initialization: the root 
file:///home/svensson/apache-jena-fuseki-3.10.0/run/configuration/service1.ttl#authorities
 has no most specific type that is a subclass of ja:Object
[2019-01-15 11:14:13] WebAppContext WARN  Failed startup of context 
o.e.j.w.WebAppContext@46044faa{Apache Jena Fuseki 
Server,/,file:///home/svensson/apache-jena-fuseki-3.10.0/webapp/,UNAVAILABLE}
org.apache.jena.assembler.exceptions.NoSpecificTypeException: the root 
file:///home/svensson/apache-jena-fuseki-3.10.0/run/configuration/service1.ttl#authorities
 has no most specific type that is a subclass of ja:Object
  doing:
    root: 
file:///home/svensson/apache-jena-fuseki-3.10.0/run/configuration/service1.ttl#dnb
 with type: http://jena.hpl.hp.com/2005/11/Assembler#RDFDataset assembler 
class: class org.apache.jena.sparql.core.assembler.DatasetAssembler

Have I missed something obvious?

Thanks in advance,

Lars