Fix check for nodes not present in EdgesHandler (#2963)

lib/network/modules/EdgesHandler.js

@@ -385,8 +385,8 @@ class EdgesHandler {
     let nodeList = [];
     if (this.body.edges[edgeId] !== undefined) {
       let edge = this.body.edges[edgeId];
-      if (edge.fromId) {nodeList.push(edge.fromId);}
-      if (edge.toId)   {nodeList.push(edge.toId);}
+      if (edge.fromId !== undefined) {nodeList.push(edge.fromId);}
+      if (edge.toId !== undefined)   {nodeList.push(edge.toId);}
     }
     return nodeList;
   }