@Override
    public String getValue() {
      if (this.getPattern() != null) {
        return "{" + this.separator + this.getName() + ":" + this.getPattern() + "}";
      }
      return "{" + this.separator + this.getName() + "}";
    }
Expression that adheres to Simple String Expansion as outlined in <a
href="https://tools.ietf.org/html/rfc6570#section-3.2.2>Simple String Expansion (Level 1)</a>
core/src/main/java/feign/template/Expressions.java