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### Description

<!-- Explain what you did, what you expected to happen, and what actually happened. -->

rpc uac.reg_add

Use a dot (.) if no value should be set for auth_password, auth_ha1, contact_addr, realm,or socket

### Expected behavior

https://github.com/kamailio/kamailio/blob/master/src/modules/uac/uac_reg.c#L...

``` if(reg.realm.len==1 && reg.realm.s[0] == '.') { reg.realm.s = NULL; reg.realm.len = 0; }

if(reg.socket.len==1 && reg.socket.s[0] == '.') { reg.socket.s = NULL; reg.socket.len = 0; } ```

#### Actual observed behavior

#### Debugging Data

``` (paste your debugging data here) ```

#### Log Messages

<!-- Check the syslog file and if there are relevant log messages printed by Kamailio, add them next, or attach to issue, or provide a link to download them (e.g., to a pastebin site). -->

``` (paste your log messages here) ```

#### SIP Traffic

<!-- If the issue is exposed by processing specific SIP messages, grab them with ngrep or save in a pcap file, then add them next, or attach to issue, or provide a link to download them (e.g., to a pastebin site). -->

``` (paste your sip traffic here) ```

### Possible Solutions

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### Additional Information

* **Kamailio Version** - output of `kamailio -v`

``` Master ```

* **Operating System**:

<!-- Details about the operating system, the type: Linux (e.g.,: Debian 8.4, Ubuntu 16.04, CentOS 7.1, ...), MacOS, xBSD, Solaris, ...; Kernel details (output of `uname -a`) -->

``` Debian11 ```