code: public void addDefaultHeader(final String name, final String value) {
          Validate.notEmpty(name, "header name cannot be empty");
          Validate.notNull(value, "header value cannot be null, use an empty string instead");
          this.checkConfigurable();
          this.defaultHeaders.put(name, value);
      }
docs: Adds a default header to be added to every stub http response.
  @param name header name (cannot be empty)
  @param value header value (cannot be <tt>null</tt>)