At least on Windows, Zabbix agent fails to start if Server= is commented out in the config and
StartAgents>0. It fails with error like this:

zabbix_agentd [8262]: ERROR: StartAgents is not 0, parameter "Server" must be defined

However, default comments in zabbix_agentd.conf says that this parameters is not mandatory. And there is no dependency on StartAgents documented.
Here how it looks like;

### Option: Server
# List of comma delimited IP addresses (or hostnames) of Zabbix servers.
# Incoming connections will be accepted only from the hosts listed here.
# If IPv6 support is enabled then '127.0.0.1', '::127.0.0.1', '::ffff:127.0.0.1' are treated equally.
#
# Mandatory: no
# Default:
# Server=

Please consider to change default, or document this situation more accurate.