MDEV-11143 Server crashes in json_string_set_cs.

        Some JSON functions didn't expect NULL as a path.

mysql-test/r/func_json.result

@@ -91,6 +91,9 @@ json_contains_path('{"key1":1, "key2":[2,3]}', "aLl", "$.key1", "$.key2")
 select json_contains_path('{ "a": true }', NULL, '$.a' );
 json_contains_path('{ "a": true }', NULL, '$.a' )
 NULL
+select json_contains_path('{ "a": true }', 'all', NULL );
+json_contains_path('{ "a": true }', 'all', NULL )
+NULL
 select json_extract('{"key1":"asd", "key2":[2,3]}', "$.key1");
 json_extract('{"key1":"asd", "key2":[2,3]}', "$.key1")
 "asd"

mysql-test/t/func_json.test

@@ -36,6 +36,7 @@ select json_contains_path('{"key1":1, "key2":[2,3]}', "one", "$.key1", "$.ma");
 select json_contains_path('{"key1":1, "key2":[2,3]}', "aLl", "$.key1", "$.ma");
 select json_contains_path('{"key1":1, "key2":[2,3]}', "aLl", "$.key1", "$.key2");
 select json_contains_path('{ "a": true }', NULL, '$.a' );
+select json_contains_path('{ "a": true }', 'all', NULL );
  
 select json_extract('{"key1":"asd", "key2":[2,3]}', "$.key1");
 select json_extract('{"key1":"asd", "key2":[2,3]}', "$.keyX", "$.keyY");

sql/item_jsonfunc.cc

@@ -450,6 +450,9 @@ String *Item_func_json_extract::val_str(String *str)
       c_path->parsed= c_path->constant;
     }
 
+    if (args[n_arg]->null_value)
+      goto error;
+
     json_scan_start(&je, js->charset(),(const uchar *) js->ptr(),
                     (const uchar *) js->ptr() + js->length());
 
@@ -547,6 +550,9 @@ longlong Item_func_json_extract::val_int()
       c_path->parsed= c_path->constant;
     }
 
+    if (args[n_arg]->null_value)
+      goto error;
+
     json_scan_start(&je, js->charset(),(const uchar *) js->ptr(),
                     (const uchar *) js->ptr() + js->length());
 
@@ -661,6 +667,9 @@ longlong Item_func_json_contains::val_int()
       c_path->parsed= c_path->constant;
     }
 
+    if (args[n_arg]->null_value)
+      goto error;
+
     json_scan_start(&je, js->charset(),(const uchar *) js->ptr(),
                     (const uchar *) js->ptr() + js->length());
 
@@ -768,6 +777,9 @@ longlong Item_func_json_contains_path::val_int()
       c_path->parsed= c_path->constant;
     }
 
+    if (args[n_arg]->null_value)
+      goto error;
+
     json_scan_start(&je, js->charset(),(const uchar *) js->ptr(),
                     (const uchar *) js->ptr() + js->length());
 
@@ -1946,6 +1958,9 @@ String *Item_func_json_search::val_str(String *str)
     }
   }
 
+  if (args[n_arg]->null_value)
+    goto null_return;
+
   json_scan_start(&je, js->charset(),(const uchar *) js->ptr(),
                   (const uchar *) js->ptr() + js->length());