code: function logicalOperator(queryObject, actualField, key) {
      let textQuery = '(';
  
      for (let i = 0; i < queryObject.length; i++) {
          textQuery += (i > 0 ? OPS[key] : '') + stringify(queryObject[i], actualField);
      }
  
      return textQuery + ')';
  }
docs: Converts logical operator queries into string by applying operator and
  recursively invokes parsing process for rvalue.
  
  @param {object} queryObject Which contains the operator.
  @param {string} actualField Current field of the object which the filter is operating on.
  @param {string} key Should be '$and' or '$or'. The current operation key.
  @returns {string}