scala：无法检查匹配的不可达性

但是下面的代码提出了这个警告：

def toConditionOperator(value: String): ConditionOperator.Value = {
  if (value==null) {
    ConditionOperator.Unknown
  } else {
    value.toLowerCase match {
      case "equal" | "=" | ":"             => ConditionOperator.Equal
      case "notequal" | "!=" | "!:" | "<>" => ConditionOperator.NotEqual
      case "greaterorequal" | ">="         => ConditionOperator.GreaterOrEqual
      case "greater" | ">"                 => ConditionOperator.Greater
      case "lessorequal" | "<="            => ConditionOperator.LessOrEqual
      case "less" | "<"                    => ConditionOperator.Less
      case "between"                       => ConditionOperator.Between
      case "in"                            => ConditionOperator.In
      case "startswith"                    => ConditionOperator.StartsWith
      case "endswith"                      => ConditionOperator.EndsWith
      case "contains" | "$"                => ConditionOperator.Contains
      case "missing" | ""                  => ConditionOperator.Missing
      case "unknown" | _                   => ConditionOperator.Unknown
    }
  }
}


[info] Compiling 98 Scala sources and 2 Java sources to /home/sas/tmp/ideas-ba/webservice/target/scala-2.10/classes...
[warn] /home/sas/tmp/ideas-ba/webservice/app/utils/query/ConditionParser.scala:203: Cannot check match for unreachability.
[warn] (The analysis required more space than allowed. Please try with scalac -Dscalac.patmat.analysisBudget=512 or -Dscalac.patmat.analysisBudget=off.)
[warn]       value.toLowerCase match {
[warn]             ^

在Play 2.0.4(使用scala 2.9.1)中它工作正常,使用此版本(scala 2.10)它会产生此警告

知道什么可能是错的吗？