#### Pre-Submission Checklist - [x] Commit message has the format required by CONTRIBUTING guide - [x] Commits are split per component (core, individual modules, libs, utils, ...) - [x] Each component has a single commit (if not, squash them into one commit) - [x] No commits to README files for modules (changes must be done to docbook files in `doc/` subfolder, the README file is autogenerated)

#### Type Of Change - [ ] Small bug fix (non-breaking change which fixes an issue) - [x] New feature (non-breaking change which adds new functionality) - [ ] Breaking change (fix or feature that would change existing functionality)

#### Checklist: - [x] PR should be backported to stable branches - [x] Tested changes locally - [x] Related to issue #1378

#### Description

- allow custom cdr fields defined with cdr_extra modparam to be saved as null. Before this change, cdr_extra variables not defined in config operation (or set to $null) were saved as empty string (''). This commit makes possible to save them as NULL value.

- new modparam to make this behaviour configurable: cdr_extra_nullable. Set it to 1 to enable this new behaviour (default value: 0) You can view, comment on, or merge this pull request online at:

https://github.com/kamailio/kamailio/pull/1385

-- Commit Summary --

* acc: Allow nullable cdr extra fields

-- File Changes --

M src/modules/acc/acc_cdr.c (11) M src/modules/acc/acc_mod.c (8) M src/modules/acc/acc_mod.h (1) M src/modules/acc/doc/acc_admin.xml (22)

-- Patch Links --

https://github.com/kamailio/kamailio/pull/1385.patch https://github.com/kamailio/kamailio/pull/1385.diff