fix npe for setting directed flag (#58)

* fix npe for setting directed flag

* fix data struct

Author: Nicole00

nebula-algorithm/src/main/scala/com/vesoft/nebula/algorithm/lib/Node2vecAlgo.scala

@@ -155,11 +155,14 @@ object Node2vecAlgo {
     graph = Graph(indexedNodes, indexedEdges)
       .mapVertices[NodeAttr] {
         case (vertexId, clickNode) =>
-          val (j, q)        = this.setupAlias(clickNode.neighbors)
-          val nextNodeIndex = this.drawAlias(j, q)
-          clickNode.path = Array(vertexId, clickNode.neighbors(nextNodeIndex)._1)
-
-          clickNode
+          if (clickNode != null) {
+            val (j, q)        = this.setupAlias(clickNode.neighbors)
+            val nextNodeIndex = this.drawAlias(j, q)
+            clickNode.path = Array(vertexId, clickNode.neighbors(nextNodeIndex)._1)
+            clickNode
+          } else {
+            NodeAttr()
+          }
       }
       .mapTriplets { edgeTriplet: EdgeTriplet[NodeAttr, EdgeAttr] =>
         val (j, q) = this.setupEdgeAlias(bcP.value, bcQ.value)(edgeTriplet.srcId,
@@ -210,11 +213,14 @@ object Node2vecAlgo {
           .map {
             case (edge, ((srcNodeId, pathBuffer), attr)) =>
               try {
-                val nextNodeIndex = this.drawAlias(attr.J, attr.q)
-                val nextNodeId    = attr.dstNeighbors(nextNodeIndex)
-                pathBuffer.append(nextNodeId)
-
-                (srcNodeId, pathBuffer)
+                if (pathBuffer != null && pathBuffer.nonEmpty && attr.dstNeighbors != null && attr.dstNeighbors.nonEmpty) {
+                  val nextNodeIndex = this.drawAlias(attr.J, attr.q)
+                  val nextNodeId    = attr.dstNeighbors(nextNodeIndex)
+                  pathBuffer.append(nextNodeId)
+                  (srcNodeId, pathBuffer)
+                } else {
+                  (srcNodeId, pathBuffer)
+                }
               } catch {
                 case e: Exception => throw new RuntimeException(e.getMessage)
               }