Don't add packages list if there are no packages
MODIFY
repo2docker/detectors.py
repo2docker/detectors.py
@@ -54,6 +54,7 @@ RUN apt-get update && \
apt-get clean && \
rm -rf /var/lib/apt/lists/*
+{% if packages -%}
RUN apt-get update && \
apt-get install --yes \
{% for package in packages -%}
@@ -62,6 +63,7 @@ RUN apt-get update && \
&& apt-get purge && \
apt-get clean && \
rm -rf /var/lib/apt/lists/*
+{% endif -%}
EXPOSE 8888

Don't add packages list if there are no packages