Less compiler error reporting broken for imported files

https://github.com/playframework/playframework/commit/cacfb8475109720c6e3ab1b3057983348bc97495 broke error reporting for Less compilation in master. I very much would like to see Less upgraded to 1.4.1 (or actually 1.4.2), but it looks like there's some problems still

    play.PlayExceptions$UnexpectedException: Unexpected exception[EcmaError: TypeError: Cannot call method "toCSS" of undefined (compiler.js#40)]
        at play.PlayReloader$$anon$1$$anonfun$reload$2$$anonfun$apply$14.apply(PlayReloader.scala:309) ~[na:na]
        at play.PlayReloader$$anon$1$$anonfun$reload$2$$anonfun$apply$14.apply(PlayReloader.scala:298) ~[na:na]
        at scala.Option.map(Option.scala:145) ~[scala-library.jar:na]
        at play.PlayReloader$$anon$1$$anonfun$reload$2.apply(PlayReloader.scala:298) ~[na:na]
        at play.PlayReloader$$anon$1$$anonfun$reload$2.apply(PlayReloader.scala:296) ~[na:na]
        at scala.util.Either$LeftProjection.map(Either.scala:377) ~[scala-library.jar:na]
    org.mozilla.javascript.EcmaError: TypeError: Cannot call method "toCSS" of undefined (compiler.js#40)
        at org.mozilla.javascript.ScriptRuntime.constructError(ScriptRuntime.java:3687) ~[na:na]
        at org.mozilla.javascript.ScriptRuntime.constructError(ScriptRuntime.java:3665) ~[na:na]
        at org.mozilla.javascript.ScriptRuntime.typeError(ScriptRuntime.java:3693) ~[na:na]
        at org.mozilla.javascript.ScriptRuntime.typeError2(ScriptRuntime.java:3712) ~[na:na]
        at org.mozilla.javascript.ScriptRuntime.undefCallError(ScriptRuntime.java:3731) ~[na:na]
        at org.mozilla.javascript.ScriptRuntime.getPropFunctionAndThisHelper(ScriptRuntime.java:2258) ~[na:na]