isEmptyValueDirective(node, context) {
    if (node.value == null) {
      return false
    }
    if (node.value.expression != null) {
      return false
    }

    let valueText = context.getSourceCode().getText(node.value)
    if (
      (valueText[0] === '"' || valueText[0] === "'") &&
      valueText[0] === valueText[valueText.length - 1]
    ) {
      // quoted
      valueText = valueText.slice(1, -1)
    }
    if (!valueText) {
      // empty
      return true
    }
    return false
  }
Check whether the given directive attribute has their empty value (`=""`).
@param {VDirective} node The directive attribute node to check.
@param {RuleContext} context The rule context to use parser services.
@returns {boolean} `true` if the directive attribute has their empty value (`=""`).