Issue Summary

It's not possible to define plan variable with empty value as YAML Specs doesn't support empty String nodes.

Java Specs allows to configure variable with empty value

See https://community.atlassian.com/t5/Bamboo-questions/BUG-How-to-declare-an-emtpy-variable-in-Bamboo-YAML-specs/qaq-p/1439865 for details

Steps to Reproduce

1. Create YAML file and define plan variable with empty value
2. Push change to repository

Expected Results

Plan created and variable has empty value

Actual Results

Specs processing fails.

Workaround

Use dummy value and handle it when analyze variable value.