With non Oracle DB macro expansion with empty string value will succeed but with Oracle DB will fail.

In most cases zbx_db_is_null() is used for checking various IDs where the value of type zbx_uint64_t can't be an empty string. However there are multiple places where this check is used for values that could be empty strings and not equal to NULL.

src/libs/zbxserver/expression.c:

1)

Observed:
With MySQL if a discovered host has no DNS macros {DISCOVERY.DEVICE.DNS} expansion will succeed (same with {HOST.METADATA}) and the replaced value would be an empty string. However with Oracle DB in the same scenario macros expansion will fail.

Expected:
Identical behaviour with all DBa - no need to fail macro expansion if field is empty (like dservices.dns) or has no data and is NULL (like drules.proxy_hostid). Those are normal situation.

DBget_dhost_value_by_event()

• tables: drule, dservices

-       if (NULL != (row = DBfetch(result)) && SUCCEED != DBis_null(row[0]))
+       if (NULL != (row = DBfetch(result)))
        {
-               *replace_to = zbx_strdup(*replace_to, row[0]);
+               *replace_to = zbx_strdup(*replace_to, ZBX_NULL2STR(row[0]));

get_autoreg_value_by_event()

• table: autoreg_host

-               if (SUCCEED == DBis_null(row[0]))
-               {
-                       zbx_free(*replace_to);
-               }
-               else
-                       *replace_to = zbx_strdup(*replace_to, row[0]);
-
+               *replace_to = zbx_strdup(*replace_to, ZBX_NULL2STR(row[0]));

2)

DBget_drule_value_by_event()

• table: drule
  • field: name

For macro expansion only name field is used. It cannot be NULL and without manually changing DB it also cannot be empty. No need for DBis_null() check.

-       if (NULL != (row = DBfetch(result)) && SUCCEED != DBis_null(row[0]))
+       if (NULL != (row = DBfetch(result)))