我有一个 Dockerfile，需要从命令行获取基本映像标签并动态加载它，但我使用此命令行收到此错误。
$ docker build --network=host --build-arg sample_TAG=7.0 --rm=true .
Step 9/12 : FROM "${sample_TAG}"
base name ("${sample_TAG}") should not be blank
Docker 文件：
FROM maven:3.6.1-jdk-8 as maven-build
ARG sample_TAG
ENV LANG en_US.UTF-8
ENV LANGUAGE en_US:en
ENV LC_ALL en_US.UTF-8
WORKDIR /apps/sample-google
COPY . /apps/sample-google
RUN mvn clean package
RUN echo "image tag is ${sample_TAG}"
FROM $sample_TAG
VOLUME /apps
RUN mkdir /apps/sample-google
COPY --from=maven-build /apps/sample-google/target /apps/sample-google
echo 行正确打印“最新”字符串，但在“FROM $sample_TAG”行中失败。