Passing a String to the == (Core eq) operator throws a JaninoRuntimeException

[MLnick]

This throws an exception with the following warning:
org.codehaus.janino.JaninoRuntimeException: Incompatible return types

This can be reproduced with the following code

    val action = core.eq(inputExpr, "cat")
    val pfaDoc = new PFABuilder()
      .withInput[String]
      .withOutput[Boolean]
      .withAction(action)
      .pfa
    val engine = getPFAEngine(pfaDoc.toJSON())
    engine.action(engine.jsonInput("cat"))