Update 'a3/binary_search_tree.c'

a3/binary_search_tree.c

@@ -59,6 +59,8 @@ void free_tree(node_t *tree) {
 
 // Function to return sorted data from the binary search tree
 int *sorted_data(node_t *tree) {
-
+if(tree==NULL){
+    return NULL;
+}
     return NULL;
 }