-D flag needed when converting between Dockerfile that uses useradd to one that uses adduser

[aaronhmiller]

Starting with a Debian-based Dockerfile, I ran dfc to convert it and this line:
RUN useradd -m -s /bin/bash appuser
was changed to:
RUN adduser --shell /bin/bash appuser

However, without manually adding -D building the image will fail as follows:

RUN adduser --shell /bin/bash appuser:
0.131 passwd: password for appuser is unchanged
0.131 Changing password for appuser
0.131 New password:

whereupon the job does not complete successfully. The -D allows useradd to not assign a password and the build completes properly.

The request is for the dfc tool to insert the -D flag when converting to adduser syntax.