Method empty() is ambiguous for type List

I am trying to build Orbeon Forms in Eclipse IDE.  
I get two compile errors:
"The method empty() is ambiguous for the type List"

One error is in XFormsModel.java line 991.
The other error is in XFormsModelSubmission.java at line 1359.

The XFormsModel.java code (lines 990 - 992) is:
    public Seq<EventListener> getListeners(String eventName) {
        return scala.collection.immutable.List.empty();
    }

The XFormsModelSubmission.java code (lines 1358 - 1360) is:
    public Seq<EventListener> getListeners(String eventName) {
        return scala.collection.immutable.List.empty();
    }

Each of these classes inherits the same method getListeners(String) from
XFormsEventObserver.scala.  XFormsEventObserver.scala contains this code:
--------------------------------------------------
package org.orbeon.oxf.xforms.event

import scala.collection.Seq

/**
 * Represents an event observer. Implemented by controls, xforms:model,
xforms:instance, xforms:submission.
 */
trait XFormsEventObserver extends XFormsEventTarget {
    def addListener(eventName: String, listener: EventListener)
    def removeListener(eventName: String, listener: EventListener)
    def getListeners(eventName: String): Seq[EventListener]
}
-------------------------------------------------------
The compiler error implies that it cannot determine the type of data returned
by the empty() method. I tried casting the return to various types to no
avail. This is my first exposure to Scala and I have no idea how to proceed
other than to switch to IntelliJ.   Has anyone encountered this or have a
suggestion about how to correct the problem?

I am able to use the "ant orbeon-war" target to build the application in the
same directory I use for Eclipse.

I am working in the following environment:

Orbeon-3.9.0.post.201208140745-PE
Java jdk1.6.0_27
Eclipse Helios Service Release 2 (IDE for Java EE Developers
1.3.2.20110301-1807)
Eclipse Compiler compliance level:  1.6
Generated .class files compatibility: 1.6 (I tried 1.5, but still had "the
method empty() ambiguous..." errors.)
Source compatibility:  1.6 (I tried 1.5, but still had "the method empty()
ambiguous..." errors.)
Scala IDE for Eclipse dev 2.0.2.v_09-201207120929-81d0972 and the corresponding
Scala IDE for Eclipse dev support and for Eclipse Source.
The Scala Library in my buildpath is 2.9.2.
I am running on Windows 7 Professional OS.

Thanks to anyone who may have a recommendation.


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