JSON validation behavior

Hi

We have some json regression tests in src/test/regress/expected/json_encoding_1.out with \u0000 symbol

select json '{ "a":  "null \u0000 escape" }' as not_unescaped;
         not_unescaped          
--------------------------------
 { "a":  "null \u0000 escape" }
(1 row)

select json '{ "a":  "null \u0000 escape" }' ->> 'a' as fails;
ERROR:  unsupported Unicode escape sequence
DETAIL:  \u0000 cannot be converted to text.
CONTEXT:  JSON data, line 1: { "a":...

Well, requested text type can not have \u0000 byte. But seems strange: we test json type with this value but raise same
errorfor -> operator:
 

melkij=> select json '{ "a": "null \u0000 escape"}' -> 'a' as fails;
ERROR:  unsupported Unicode escape sequence
DETAIL:  \u0000 cannot be converted to text.
CONTEXT:  JSON data, line 1: { "a":...

Result was requested in json datatype, like 'SELECT '"\u0000"'::json;' from tests before.
Similar error with access by different key:

melkij=> select json '{ "a": "null \u0000 escape", "b":1 }' ->>'b' as fails;
ERROR:  unsupported Unicode escape sequence
DETAIL:  \u0000 cannot be converted to text.
CONTEXT:  JSON data, line 1: { "a":...

We allow write such json to table, we allow read whole json, but we can not use native operators. Is this behavior
expected?

regards, Sergei