Docker build error while building a kafka-connect 5.5.0 docker image

Getting this error while building the docker image for kafka-connect:5.5.0 custom docker image.
I do have "apt-get update" in necessary locations. Anyone has a clue on how to resolve this?

W: Duplicate sources.list entry
stable/main amd64 Packages
W: You may want to run apt-get update to correct these problems

Source: Docker Questions