JS: Add some missing getContainer() predicates

javascript/ql/lib/semmle/javascript/dataflow/DataFlow.qll

@@ -765,6 +765,8 @@ module DataFlow {
     override Node getRhs() { result = TValueNode(prop.getParameter()) }
 
     override ControlFlowNode getWriteNode() { result = prop.getParameter() }
+
+    override StmtContainer getContainer() { parameter_fields(prop, result, _) }
   }
 
   /**
@@ -962,6 +964,12 @@ module DataFlow {
 
     override BasicBlock getBasicBlock() { result = function.getExit().getBasicBlock() }
 
+    override StmtContainer getContainer() {
+      // Override this to ensure a container exists even for unreachable returns,
+      // since an unreachable exit CFG node will not have a basic block
+      result = function
+    }
+
     /**
      * Gets the function corresponding to this exceptional return node.
      */
@@ -988,6 +996,12 @@ module DataFlow {
 
     override BasicBlock getBasicBlock() { result = function.getExit().getBasicBlock() }
 
+    override StmtContainer getContainer() {
+      // Override this to ensure a container exists even for unreachable returns,
+      // since an unreachable exit CFG node will not have a basic block
+      result = function
+    }
+
     /**
      * Gets the function corresponding to this return node.
      */
@@ -1386,6 +1400,8 @@ module DataFlow {
     }
 
     override string toString() { result = this.getTag().toString() }
+
+    override StmtContainer getContainer() { result = this.getTag().getInnerTopLevel() }
   }
 
   /**