reintroduce DataFlowType - otherwise nothing in the old DataFlow library would compile

python/ql/lib/semmle/python/dataflow/old/TaintTracking.qll

@@ -664,6 +664,14 @@ module DataFlow {
   }
 }
 
+deprecated private class DataFlowType extends TaintKind {
+  // this only exists to avoid an empty recursion error in the type checker
+  DataFlowType() {
+    this = "Data flow" and
+    1 = 2
+  }
+}
+
 pragma[noinline]
 private predicate dict_construct(ControlFlowNode itemnode, ControlFlowNode dictnode) {
   dictnode.(DictNode).getAValue() = itemnode