Analysing the snippet in previous comment, there is a bug obviously, probably the acc function was looked up by the fixup function, not by mod init -- in the `get_redirect_fixup()` function the condition is:
``` /* must import the acc stuff */ if (acc_fct_s==0 || acc_fct_s[0]==0) { LM_ERR("acc support enabled, but no acc function defined\n"); return E_UNSPEC; } ``` So, the bug could have been the reason to not require empty value for acc function parameter to disable acc.