private void validateMap(Map<String, String> env) {
        for (Map.Entry<String,String> entry : env.entrySet()) {
            if (entry.getValue() == null || entry.getValue().length() == 0) {
                throw new IllegalArgumentException("Environment variable '" +
                                                   entry.getKey() + "' must not be null or empty if building an image");
            }
        }
    }
Adds the RUN Commands within the build image section
@param runCmds
@return
src/main/java/io/fabric8/maven/docker/assembly/DockerFileBuilder.java