Python: Fix default parameter value flow

Somehow the previous fix didn't work :O

Author: RasmusWL

python/ql/lib/semmle/python/dataflow/new/internal/DataFlowPrivate.qll

@@ -467,8 +467,10 @@ predicate runtimeJumpStep(Node nodeFrom, Node nodeTo) {
   // a parameter with a default value, since the parameter will be in the scope of the
   // function, while the default value itself will be in the scope that _defines_ the
   // function.
-  nodeFrom.(CfgNode).getNode() =
-    nodeTo.(EssaNode).getVar().getDefinition().(ParameterDefinition).getDefault()
+  exists(ParameterDefinition param |
+    nodeFrom.asCfgNode() = param.getDefault() and
+    nodeTo.asCfgNode() = param.getDefiningNode()
+  )
 }
 
 /**

python/ql/test/library-tests/PointsTo/new/ImpliesDataflow.expected

@@ -1,7 +1,5 @@
 | code/h_classes.py:3:1:3:16 | ControlFlowNode for ClassExpr | code/h_classes.py:10:1:10:9 | ControlFlowNode for type() |
 | code/h_classes.py:3:1:3:16 | ControlFlowNode for ClassExpr | code/h_classes.py:15:5:15:13 | ControlFlowNode for type() |
-| code/l_calls.py:3:13:3:14 | ControlFlowNode for List | code/l_calls.py:4:12:4:12 | ControlFlowNode for x |
-| code/l_calls.py:6:13:6:14 | ControlFlowNode for List | code/l_calls.py:7:16:7:16 | ControlFlowNode for x |
 | code/l_calls.py:12:1:12:20 | ControlFlowNode for ClassExpr | code/l_calls.py:16:16:16:18 | ControlFlowNode for cls |
 | code/l_calls.py:12:1:12:20 | ControlFlowNode for ClassExpr | code/l_calls.py:24:13:24:22 | ControlFlowNode for Attribute() |
 | code/l_calls.py:12:1:12:20 | ControlFlowNode for ClassExpr | code/l_calls.py:25:16:25:16 | ControlFlowNode for a |