kotlin no-null crash fix

Author: guaishouN

library/src/main/java/com/gyso/treeview/layout/TreeLayoutManager.java

@@ -138,7 +138,9 @@ public void setViewport(int winHeight, int winWidth) {
      * path->path from parent, same as paint
      */
     public void performDrawLine(DrawInfo drawInfo){
-        baseline.draw(drawInfo);
+        if(baseline!=null){
+            baseline.draw(drawInfo);
+        }
     }
 
     /**

library/src/main/java/com/gyso/treeview/listener/TreeViewControlListener.java

@@ -2,6 +2,8 @@
 
 import android.view.View;
 
+import androidx.annotation.Nullable;
+
 import com.gyso.treeview.model.NodeModel;
 
 /**
@@ -17,5 +19,5 @@ public interface TreeViewControlListener {
     int FREE_SCALE = 0;
     int MAX_SCALE  = 1;
     void onScaling(int state, int percent);
-    void onDragMoveNodesHit(NodeModel<?> draggingNode, NodeModel<?> hittingNode, View draggingView, View hittingView);
+    void onDragMoveNodesHit(@Nullable NodeModel<?> draggingNode, @Nullable NodeModel<?> hittingNode, @Nullable View draggingView, @Nullable View hittingView);
 }