def cssClass: Option[String] = None

scala> def listTemplate: NodeSeq = <table class={cssClass.map(Text(_))}></table>
listTemplate: scala.xml.NodeSeq

scala> val func = "#headerxx_item" #> "x"
func: net.liftweb.util.CssSel = CssBind(Full(#headerxx_item), Full(IdSelector(headerxx_item,Empty)))

scala> func(listTemplate)
java.lang.NullPointerException
at scala.xml.NodeSeq.iterator(NodeSeq.scala:51)
at scala.collection.IterableLike$class.foreach(IterableLike.scala:73)
at scala.xml.NodeSeq.foreach(NodeSeq.scala:43)
at scala.collection.TraversableLike$class.map(TraversableLike.scala:194)
at scala.xml.NodeSeq.map(NodeSeq.scala:43)
at scala.xml.NodeSeq.text(NodeSeq.scala:152)
at scala.xml.MetaData$$anonfun$asAttrMap$1.apply(MetaData.scala:168)
at scala.xml.MetaData$$anonfun$asAttrMap$1.apply(MetaData.scala:168)
at scala.collection.Iterator$$anon$19.next(Iterator.scala:335)
at scala.collection.Iterator$class.foreach(Iterator.scala:660)
at scala.collection.Iterator$$anon$19.foreach(Iterator.scala:333)
at scala.collection.TraversableOnce$class.toMap(TraversableOnce.scala:256)
at scala.collection.Iterator$$anon$19.toMap(Iterator.scala:333)
at scala.xml.MetaData.asAttrMap(MetaData.scala:168)
at scala.xml.MetaData.strict_$eq$eq(MetaData.scala:137)
at scala.xml.Equality$class.doComparison(Equality.scala:103)
at scala.xml.Equality$class.equals(Equality.scala:92)
at scala.xml.MetaData.equals(MetaData.scala:74)
at net.liftweb.util.SelectorMap.slurpAttrs(BindHelpers.scala:2291)
at net.liftweb.util.SelectorMap.net$liftweb$util$SelectorMap$$treatElem(BindHelpers.scala:2324)
at net.liftweb.util.SelectorMap$$anonfun$net$liftweb$util$SelectorMap$$run$1.apply(BindHelpers.scala:2386)
at net.liftweb.util.SelectorMap$$anonfun$net$liftweb$util$SelectorMap$$run$1.apply(BindHelpers.scala:2384)
at scala.collection.TraversableLike$$anonfun$flatMap$1.apply(TraversableLike.scala:200)
at scala.collection.TraversableLike$$anonfun$flatMap$1.apply(TraversableLike.scala:200)
at scala.collection.Iterator$class.foreach(Iterator.scala:660)
at scala.collection.LinearSeqLike$$anon$1.foreach(LinearSeqLike.scala:50)
at scala.collection.IterableLike$class.foreach(IterableLike.scala:73)
at scala.xml.NodeSeq.foreach(NodeSeq.scala:43)
at scala.collection.TraversableLike$class.flatMap(TraversableLike.scala:200)
at scala.xml.NodeSeq.flatMap(NodeSeq.scala:43)
at net.liftweb.util.SelectorMap.net$liftweb$util$SelectorMap$$run(BindHelpers.scala:2384)
at net.liftweb.util.SelectorMap.apply(BindHelpers.scala:2380)
at net.liftweb.util.CssBind$class.apply(BindHelpers.scala:2405)
at net.liftweb.util.CssBindImpl.apply(BindHelpers.scala:2461)
at net.liftweb.util.CssBindImpl.apply(BindHelpers.scala:2461)
at .<init>(<console>:21)
at .<clinit>(<console>)
at .<init>(<console>:11)
at .<clinit>(<console>)
at $print(<console>)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:704)
at scala.tools.nsc.interpreter.IMain$Request$$anonfun$14.apply(IMain.scala:920)
at scala.tools.nsc.interpreter.Line$$anonfun$1.apply$mcV$sp(Line.scala:43)
at scala.tools.nsc.io.package$$anon$2.run(package.scala:25)
at java.lang.Thread.run(Thread.java:680)

I realize I can use transforms to achieve this, but this was existing code :-)