MDEV-11450 Assertion `!null_value' failed invirtual bool Item::send on json_search.

        Item_func_json_search::val_str didn't set the null_value
        properly. So that affected the next record in the resultset.

mysql-test/r/func_json.result

@@ -217,6 +217,15 @@ json_search(@j, 'all', '10', NULL, '$[*]')
 select json_search(@j, 'all', '10', NULL, '$[*][0].k');
 json_search(@j, 'all', '10', NULL, '$[*][0].k')
 "$[1][0].k"
+create table t1( json_col text );
+insert into t1 values
+('{ "a": "foobar" }'),
+('{ "a": "foobar", "b": "focus", "c": [ "arm", "foot", "shoulder" ] }');
+select json_search( json_col, 'all', 'foot' ) from t1;
+json_search( json_col, 'all', 'foot' )
+NULL
+"$.c[1]"
+drop table t1;
 select json_unquote('"abc"');
 json_unquote('"abc"')
 abc

mysql-test/t/func_json.test

@@ -92,6 +92,12 @@ select json_search(@j, 'all', 'abc', NULL, '$');
 select json_search(@j, 'all', '10', NULL, '$');
 select json_search(@j, 'all', '10', NULL, '$[*]');
 select json_search(@j, 'all', '10', NULL, '$[*][0].k');
+create table t1( json_col text );
+insert into t1 values
+('{ "a": "foobar" }'),
+  ('{ "a": "foobar", "b": "focus", "c": [ "arm", "foot", "shoulder" ] }');
+select json_search( json_col, 'all', 'foot' ) from t1;
+drop table t1;
 
 
 select json_unquote('"abc"');

sql/item_jsonfunc.cc

@@ -1964,11 +1964,10 @@ String *Item_func_json_search::val_str(String *str)
         goto error;
       c_path->parsed= c_path->constant;
     }
+    if (args[n_arg]->null_value)
+      goto null_return;
   }
 
-  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());
 
@@ -2063,6 +2062,7 @@ String *Item_func_json_search::val_str(String *str)
       goto error;
   }
 
+  null_value= 0;
   return str;