Selecting graphs in GraphDB using filter exists does not seem to work

Question

I am running a query to select all graphs using filter exists, like this

SELECT * WHERE {
  graph ?g { filter exists { ?s ?p ?o  } }
} 

but its response is

{
  "head": {
    "vars": [
      "g"
    ]
  },
  "results": {
    "bindings": [
      {}
    ]
  }
}

and I am pretty sure that the triplestore store has graphs.

Note: the more classic query works but takes a while, so I was hoping this would improve performance.

select distinct ?g where { 
    graph ?g {
         ?s ?p ?o 
    }
} 

I double-checked on Jena Fuseki and there the filter exists works.