get a error in Step 6

[jerome-peng]

i use win10+vbox+boot2docker.iso

when i build, get a error in step 6:

docker@default:~$ docker build . -t ora2pg
Sending build context to Docker daemon 20.48kB
Step 1/23 : FROM perl:slim
---> 327e48466da5
Step 2/23 : ARG ORA2PG_VERSION=19.0
---> Using cache
---> 66f5dc3d44f4
Step 3/23 : RUN mkdir -p /usr/share/man/man1 && mkdir -p /usr/share/man/man7
---> Using cache
---> 73a3935d2563
Step 4/23 : RUN apt update && apt install -y unzip rpm alien libaio1 postgresql-client libdbi-perl bzip2
---> Using cache
---> 7d2bbb8bf8ca
Step 5/23 : RUN curl -L -o /tmp/ora2pg.zip https://github.com/darold/ora2pg/archive/v$ORA2PG_VERSION.zip && (cd /tmp && unzip ora2pg.zip && rm -f ora2pg.zip) && mv /tmp/ora2pg* /tmp/ora2pg && (cd /tmp/ora2pg && perl Makefile.PL && make && make install)
---> Using cache
---> 0b121a6e1b3a
Step 6/23 : ADD /assets /assets
ADD failed: stat /mnt/sda1/var/lib/docker/tmp/docker-builder457884445/assets: no such file or directory