public Builder addEnvironment(@Nullable Map<String, String> environment) {
      if (environment != null) {
        environmentBuilder.putAll(environment);
      }
      return this;
    }
Adds a map of environment variables to the current map.

@param environment the map of environment variables
@return this
jib-core/src/main/java/com/google/cloud/tools/jib/image/Image.java