Use indentation level reported by checkstyle

dolphinscheduler-common/src/main/java/org/apache/dolphinscheduler/common/graph/DAG.java

@@ -433,11 +433,9 @@ public class DAG<Node, NodeInfo, EdgeInfo> {
    */
   private Set<Node> getNeighborNodes(Node node, final Map<Node, Map<Node, EdgeInfo>> edges) {
         final Map<Node, EdgeInfo> neighborEdges = edges.get(node);
-
         if (neighborEdges == null) {
             return Collections.emptySet();
         }
-
         return neighborEdges.keySet();
   }