ParallelMux: assert inputs are not empty

src/main/scala/utils/ParallelMux.scala

@@ -5,6 +5,7 @@ import chisel3.util._
 
 object ParallelOperation {
   def apply[T <: Data](xs: Seq[T], func: (T, T) => T): T = {
+    require(xs.nonEmpty)
     xs match {
       case Seq(a) => a
       case Seq(a, b) => func(a, b)
@@ -37,4 +38,4 @@ object ParallelLookUp {
   def apply[T<:Data](key: UInt, mapping:Seq[(UInt,T)]): T = {
     ParallelMux(mapping.map(m => (m._1===key) -> m._2))
   }
-}
\ No newline at end of file
+}