Javadoc: error - no public or protected classes were found for the document

Question

Before causing a problem when running javadoc in a child project. There are several projects, and they are interdependent.

When running javadoc in childproject, I get an error below when other project classes (dependent classes for the child project) are not found in the pathpath. javadoc: error - no public or protected classes were found for the document.

How to run javadoc in childproject? Looked at javadoc options that didn't help.

thanks