old_contents: import sys
  import os
  import yaml
  from jinja2 import Environment, FileSystemLoader
  
  def env_override(value, key):
    return os.getenv(key, value)
  
  def main():
      jinja = Environment(loader=FileSystemLoader("."))
      jinja.filters['env'] = env_override
  
      template = jinja.get_template("meta-compose.yml")
  
      with open("meta-compose-data.yml", "r") as fh:
          data = yaml.safe_load(fh)
  
      composition = template.render(data)
  
      with open("docker-compose.yml", "w") as fh:
          fh.write(composition)
  
new_contents: import sys
  import os
  import yaml
  from jinja2 import Environment, FileSystemLoader
  
  def env_override(value, key):
    return os.getenv(key, value)
  
  def main():
  
      template_file_name = "meta-compose.yml"
      data_file_name = "meta-compose-data.yml"
  
      jinja = Environment(loader=FileSystemLoader("."))
      jinja.filters['env'] = env_override
  
      template = jinja.get_template(template_file_name)
  
  
      if os.path.isfile(data_file_name):
          with open(data_file_name, "r") as fh:
              data = yaml.safe_load(fh)
      else:
          data = {}
  
      composition = template.render(data)
  
      with open("docker-compose.yml", "w") as fh:
          fh.write(composition)
  
subject: fix error when no meta-compose-data.yml present