Minor: OpaqueBytes should never be empty. May catch certain types of simple mistake.

src/core/Utils.kt

@@ -7,6 +7,8 @@ import java.util.*
 
 /** A simple class that wraps a byte array and makes the equals/hashCode/toString methods work as you actually expect */
 open class OpaqueBytes(val bits: ByteArray) : SerializeableWithKryo {
+    init { check(bits.isNotEmpty()) }
+
     companion object {
         fun of(vararg b: Byte) = OpaqueBytes(byteArrayOf(*b))
     }