Import Error error: package org.sleuthkit.autopsy

We are making a development environment on net bans java to make our own content viewer for media attachment and doing so there is an error in importing content viewer from the main autopsy github repo
error: package org.sleuthkit.autopsy.contentviewers.artifactviewers does not exist
This error is inside the Mssage artifact viewer file which i have imported in my main Attachment Message artifact viewer