title: Creating a service failed with "No command specified"
body: <p>I am very new in the container world. 
  I am trying to get the ora2pg to up and running with the help of docker_composer, but I get the following error message:</p>
  
  <blockquote>
    <p>postgres_db is up-to-date</p>
    
    <p>Creating ora2pg_client ... error</p>
    
    <p>ERROR: for ora2pg_client  Cannot create container for service ora2pg: No command specified</p>
    
    <p>ERROR: for ora2pg  Cannot create container for service ora2pg: No command specified</p>
    
    <p>ERROR: Encountered errors while bringing up the project.</p>
  </blockquote>
  
  <p>My docker-composer.yml is as below:</p>
  
  <pre><code>version: "3.7"
  services:
   postgresql:
    restart: always
    image: postgres
    container_name: "postgres_db"
    ports:
    - "5432:5432"
    environment:
    - DEBUG=false
    - DB_USER=
    - DB_PASS=
    - DB_NAME=
    - DB_TEMPLATE=
    - DB_EXTENSION=
    - REPLICATION_MODE=
    - REPLICATION_USER=
    - REPLICATION_PASS=
    - REPLICATION_SSLMODE=
    volumes:
    - ./postgres/data:/var/lib/postgresql/data
    - ./postgres/initdb:/docker-entrypoint-initdb.d
  
   ora2pg:
    image: flockers/ora2pg
    container_name: "ora2pg_client"
    environment:
    - DB_HOST=127.0.0.1
    - DB_SID=xe
    - ORA2PG_USER=MAX
    - DB_PASS=MAX
    volumes:
    - ./ora2pg/export:/export
  </code></pre>
  
  <p>Note: I already have an Oracle database on the same machine.</p>
  
  <p>Thank you!</p>