Error 500: Not in a transaction

[Laura Morales]

So, this is the Assembler file that I'm trying to use:

======================================================
PREFIX :        <#>
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.apache.org/2016/tdb#>
PREFIX ja:      <http://jena.hpl.hp.com/2005/11/Assembler#>

[] rdf:type fuseki:Server ;
   fuseki:services (
     <#service_tdb2>
   ) .

<#service_tdb2> a fuseki:Service ;
    rdfs:label          "TDB2 Service" ;
    fuseki:name         "tdb2" ;
    fuseki:serviceQuery "query", "sparql" ;
    fuseki:dataset      <#dataset> ;
    .

<#dataset> a ja:RDFDataset ;
    # tdb2:location              "" ;
    # tdb2:unionDefaultGraph     true ;
    ja:namedGraph                [ ja:graphName <http://example.org/g1> ;
                                   ja:graph     <#g1> ] ;
    .

<#g1> a tdb2:GraphTDB2 ;
    tdb2:location "g1" ;
    .
======================================================

what I'm trying to do, basically, is to have a dataset with multiple graphs but 
where each graph is located in its own location. Adding another graph would be 
(ideally) like this:

<#g2> a tdb2:GraphTDB2 ;
    tdb2:location "g2" ;
    .

With the above assembler:

# select ?g where { graph ?g {} }

this query works, I get a list of graphs

# select * from ex:g1 where { ?s ?p ?o } limit 10

this query doesn't work, I get "Error 500: Not in a transaction" but I really 
don't understand how to fix this. Is it possible to do what I'm trying to 
achive?