Problem with Mustache parboiled2 parser

gistfile1.scala

import org.parboiled2._
import scala.util.{ Success, Failure }

trait AST

case class AText(in: String) extends AST
case class AKey(in: String) extends AST
case class AEnd() extends AST

class MustacheParser(val input: ParserInput) extends Parser {
  val openS = "{{"
  val closeS = "}}"

  def open: Rule0 = rule { str(openS) }
  def close: Rule0 = rule { str(closeS) }

  def deb(in: String) = rule { run(println(s"$in ch: ${cursorChar} + i: ${cursor}")) }
  
  def NormalChar: Rule0 = rule { !(open | close) ~ deb("NC-b") ~  ANY ~ deb("NC-a") }
  def debugKeyChar(prefix: String): Rule0 = rule { !(open | close ) ~ deb(s"$prefix-b") ~  ANY ~ deb(s"$prefix-a") }
  
  def Characters: Rule0 = rule { zeroOrMore(NormalChar)  } // word
  def charsAST: Rule1[AST] = rule { capture(Characters) ~> ((s: String) => AText(s)) }
  def charsKeyAST: Rule1[AST] = rule { capture(zeroOrMore(debugKeyChar("keyChar"))) ~> ((s: String) => AKey(s))  }
  
  def KeyInner : Rule1[AST] = rule { open ~ charsKeyAST ~ close }
  def Key: Rule1[AST] = rule {deb("tried key") ~ &(open) ~ deb("Key-b") ~ KeyInner ~ deb("Key-a") }
  
  def rootRule: Rule1[Seq[AST]] = rule { zeroOrMore (Key | charsAST) ~ EOI}
}

object mymustache {

  def main (args: Array[String]): Unit = {

    val input1 = "asdasd XX asas"
    val input2 = "abcdef {{XX}} ghij"
    val input3 = "{{XX}}"
    val input4 = "{{XX1}}{{XX2}}"

    val parser = new MustacheParser(input3)
    parser.rootRule.run() match {
      case Success(a) => println("Expression is valid " + a)
      case Failure(e: ParseError) ⇒ println("Expression is not valid: " + parser.formatError(e, showTraces =  true))
      case Failure(e) => println("Unexpected error during parsing run: " + e)
    }
  }
}