anchor.diff:  * SPARQL queries with variables in the predicate position are not currently covered, with an exception of the following
   case:
   
  -[source,groovy]
  +[source,text]
   ----
   g.sparql("""SELECT * WHERE { ?x ?y ?z . }""")
   ----
  
positive.code: 
  Select all vertices with the label `person` and group them by their age.
  
  [source,groovy]
  ----
  g.sparql("""SELECT * 
  WHERE {
    ?person v:label "person" .
    ?person v:age ?age .
  
negative.code: 
  [gremlin-groovy,existing]
  ----
  g.sparql("""SELECT ?age ?software ?lang ?name
  WHERE {
    ?person v:name "josh" .
    ?person v:age ?age .
    ?person e:created ?software .
    ?software v:lang ?lang .
    ?software v:name ?name . }""")
  ----
  