Fixed edge case where a deterministic primitive call is the first executed instruction

Author: MaartenS11

src/main/kotlin/be/ugent/topl/mio/debugger/MultiverseDebugger.kt

@@ -24,12 +24,11 @@ class MultiverseGraph(var rootNode: MultiverseNode = MultiverseNode(), var curre
     fun replaceNode(node: MultiverseNode, newNode: MultiverseNode) {
         if (node == rootNode) {
             rootNode = newNode
-            return
+        } else {
+            node.parent!!.children.remove(node)
+            node.parent!!.addChild(newNode)
         }
 
-        node.parent!!.children.remove(node)
-        node.parent!!.addChild(newNode)
-
         for (child in node.children) {
             newNode.addChild(child)
         }
@@ -310,7 +309,13 @@ class MultiverseDebugger(
                 DeterministicPrimitiveNode(wasmBinary.metadata.primitive_fidx_mapping[checkpoint.fidx_called], checkpoint.args!!)
             }
 
-            graph.replaceNode(graph.currentNode.parent!!, newNode)
+            if (graph.currentNode.parent != null) {
+                graph.replaceNode(graph.currentNode.parent!!, newNode)
+            } else {
+                // Current node has no parent -> it is the root node!
+                graph.currentNode = newNode
+                graph.rootNode = newNode
+            }
         }
 
         graphUpdated()