public void addEnvironment(String name, String value) {
      if (environmentMap == null) {
        environmentMap = new HashMap<>();
      }
      environmentMap.put(name, value);
    }
Adds an environment entry to the container configuration.

@param name the environment variable key
@param value the non-null value to associate with environment variable
jib-core/src/main/java/com/google/cloud/tools/jib/configuration/ContainerConfiguration.java