@Test public void prefixes3() {

    // Some URIs without prefixes.
    String data = StrUtils.strjoinNL
        ("@prefix : <http://example/> ." ,
         "" ,
         "<http://other/s1> :p :x1 ."
         ) ;
    Graph graph1 = create(data) ;
    PrefixMapping pmap = PrefixMappingUtils.calcInUsePrefixMapping(graph1) ;
    PrefixMapping pmapExpected = new PrefixMappingImpl() ;
    pmapExpected.setNsPrefix("", "http://example/") ;
    Assert.assertTrue(sameMapping(pmapExpected, pmap)) ;
}