Steps to reproduce:

1. Install the Template according to its README
2. Increase zabbix-agent debug level to 4
3. In the agent log, look for the error "psql:/var/lib/zabbix/postgresql/pgsql.dbstat.sql:17: ОШИБКА: имя поля не может быть NULL (which means "column name cannot be NULL")

The reason of the error is the new development described in https://rjuju.github.io/postgresql/2019/04/18/new-in-pg12-statistics-checksums-errors.html

As a side effect, pg_stat_database will also now show available statistics for shared objects (such as the pg_database table for instance), in a new row with datid valued to 0, and a NULL datname. Those were always accumulated, but weren’t displayed in any system view until now.

Patch:

A simple patch solves the problem

index d874658ccc..9a6e4c4de8 100644
--- a/templates/db/postgresql/postgresql/pgsql.dbstat.sql
+++ b/templates/db/postgresql/postgresql/pgsql.dbstat.sql
@@ -14,4 +14,4 @@ SELECT json_object_agg(datname, row_to_json(T)) FROM (
                        temp_files,
                        temp_bytes,
                        deadlocks
-       FROM pg_stat_database) T
+       FROM pg_stat_database where datname is not null) T