diff --git a/src/modules/acc/acc_cdr.c b/src/modules/acc/acc_cdr.c
index f29f139e2d2..6a7862dd74e 100644
--- a/src/modules/acc/acc_cdr.c
+++ b/src/modules/acc/acc_cdr.c
@@ -238,9 +238,14 @@ static int db_write_cdr( struct dlg_cell* dialog,
 
 	for( ; i<m; i++) {
 		db_cdr_keys[i] = &cdr_attrs[i];
-		VAL_TYPE(db_cdr_vals+i)=DB1_STR;
-		VAL_NULL(db_cdr_vals+i)=0;
-		VAL_STR(db_cdr_vals+i) = cdr_value_array[i];
+
+		if (cdr_extra_nullable == 1 && cdr_type_array[i] == TYPE_NULL) {
+			VAL_NULL(db_cdr_vals + i) = 1;
+		} else {
+			VAL_TYPE(db_cdr_vals+i)=DB1_STR;
+			VAL_NULL(db_cdr_vals+i)=0;
+			VAL_STR(db_cdr_vals+i) = cdr_value_array[i];
+		}
 	}
 
 	if (df->use_table(dh, &acc_cdrs_table /*table*/) < 0) {
diff --git a/src/modules/acc/acc_mod.c b/src/modules/acc/acc_mod.c
index 2de42e8e8d8..959bd8b0cad 100644
--- a/src/modules/acc/acc_mod.c
+++ b/src/modules/acc/acc_mod.c
@@ -115,6 +115,7 @@ struct acc_extra *log_extra = 0; /*!< Log extra attributes */
 /*@{*/
 
 int cdr_enable  = 0;
+int cdr_extra_nullable  = 0;
 int cdr_log_enable  = 1;
 int cdr_start_on_confirmed = 0;
 int cdr_expired_dlg_enable = 0;
@@ -204,6 +205,7 @@ static param_export_t params[] = {
 	{"cdr_start_on_confirmed", INT_PARAM, &cdr_start_on_confirmed   },
 	{"cdr_facility",         PARAM_STRING, &cdr_facility_str           },
 	{"cdr_extra",            PARAM_STRING, &cdr_log_extra_str          },
+	{"cdr_extra_nullable",   INT_PARAM, &cdr_extra_nullable            },
 	{"cdr_start_id",	 PARAM_STR, &cdr_start_str		},
 	{"cdr_end_id",		 PARAM_STR, &cdr_end_str		},
 	{"cdr_duration_id",	 PARAM_STR, &cdr_duration_str	},
@@ -474,6 +476,12 @@ static int mod_init( void )
 		return -1;
 	}
 
+	if( cdr_extra_nullable < 0 || cdr_extra_nullable > 1)
+	{
+		LM_ERR("cdr_extra_nullable is out of range\n");
+		return -1;
+	}
+
 	if( cdr_expired_dlg_enable < 0 || cdr_expired_dlg_enable > 1)
 	{
 		LM_ERR("cdr_expired_dlg_enable is out of range\n");
diff --git a/src/modules/acc/acc_mod.h b/src/modules/acc/acc_mod.h
index 220bce41a5c..a28721cdea0 100644
--- a/src/modules/acc/acc_mod.h
+++ b/src/modules/acc/acc_mod.h
@@ -49,6 +49,7 @@ extern int log_flag;
 extern int log_missed_flag;
 
 extern int cdr_enable;
+extern int cdr_extra_nullable;
 extern int cdr_start_on_confirmed;
 extern int cdr_log_facility;
 extern int cdr_expired_dlg_enable;
diff --git a/src/modules/acc/doc/acc_admin.xml b/src/modules/acc/doc/acc_admin.xml
index e9efa8f5eaf..36022585bbd 100644
--- a/src/modules/acc/doc/acc_admin.xml
+++ b/src/modules/acc/doc/acc_admin.xml
@@ -1194,6 +1194,28 @@ modparam("acc", "cdr_facility", "LOG_DAEMON")
 ...
 modparam("acc", "cdr_extra", "c1=$dlg_var(caller);c2=$dlg_var(callee)"
 ...
+</programlisting>
+		</example>
+	</section>
+	<section id="acc.p.cdr_extra_nullable">
+		<title><varname>cdr_extra_nullable</varname> (integer)</title>
+		<para>
+		Should custom CDR fields be saved as NULL?
+		</para>
+		<para>
+		If set to 0, custom CDR fields not defined in config operation (or set to $null) will be saved as empty string.
+		If set to 1, custom CDR fields not defined in config operation (or set to $null) will be saved as NULL.
+		</para>
+		<para>
+		Default value is 0.
+		</para>
+		</para>
+		<example>
+		<title>cdr_extra_nullable example</title>
+		<programlisting format="linespecific">
+...
+modparam("acc", "cdr_extra_nullable", 1)
+...
 </programlisting>
 		</example>
 	</section>