goldmedal opened a new issue, #14884:
URL: https://github.com/apache/datafusion/issues/14884
### Describe the bug
Currenlty, if we input a null value to `to_char`, we will get an empty
string instead of a null value.
```
> select to_char(NULL, '%Y-%m-%d %H:%M:%S') is null;
+-------------------------------------------------+
| to_char(NULL,Utf8("%Y-%m-%d %H:%M:%S")) IS NULL |
+-------------------------------------------------+
| false |
+-------------------------------------------------+
1 row(s) fetched.
Elapsed 0.001 seconds.
> select to_char(NULL, '%Y-%m-%d %H:%M:%S');
+-----------------------------------------+
| to_char(NULL,Utf8("%Y-%m-%d %H:%M:%S")) |
+-----------------------------------------+
| |
+-----------------------------------------+
1 row(s) fetched.
Elapsed 0.001 seconds.
```
However, the postgres behavior is returing a null value if got a null input.
```
psql=# select to_char(null::timestamp, '%Y-%m-%d %H:%M:%S') is null;
?column?
----------
t
(1 row)
psql=# select to_char(null::timestamp, '%Y-%m-%d %H:%M:%S');
to_char
---------
(1 row)
```
I think we should follow the behavior of postgres.
### To Reproduce
Execute the SQL mentioned above.
### Expected behavior
`to_char` should return a null if got a null input.
### Additional context
_No response_
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