feat(#286): fix CI "No ClassTag available for Nothing" error

Author: arnaud-daroussin

modules/flink-common-api/src/main/scala/org/apache/flinkx/api/serializers.scala

@@ -33,6 +33,7 @@ import java.math.{BigInteger => JBigInteger}
 import java.math.{BigDecimal => JBigDecimal}
 import java.time._
 import java.util.UUID
+import scala.{Nothing => Nothing}
 import scala.collection.immutable.{SortedSet, TreeSet}
 import scala.concurrent.duration.{Duration, FiniteDuration, TimeUnit}
 import scala.reflect.{ClassTag, classTag}