Warning on advertise of std_mgs/Empty

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Recently (maybe since some update...), whenever I advertise a topic of topic std_msgs/Empty I receive WARNING:

Advertising on topic [/topic_name] with an empty message definition. Some tools (e.g. rosbag) may not work correctly.

Can I safely ignore it? Was does it mean? I often use std_msgs/Empty as kind of signal for nodes to perform long running calculations to update their state.