KAFKA-1823; Fix transient failure in PartitionAssignorTest; reviewed by Guozhang Wang and Neha Narkhede

core/src/test/scala/unit/kafka/consumer/PartitionAssignorTest.scala

@@ -187,10 +187,12 @@ private object PartitionAssignorTest extends Logging {
     // check for uniform assignment
     if (verifyAssignmentIsUniform) {
       val partitionCountForStream = partitionCountPerStream(globalAssignment)
-      val maxCount = partitionCountForStream.valuesIterator.max
-      val minCount = partitionCountForStream.valuesIterator.min
-      assertTrue("Scenario %s: assignment is not uniform (partition counts per stream are in the range [%d, %d])"
-                 .format(scenario, minCount, maxCount), (maxCount - minCount) <= 1)
+      if (partitionCountForStream.nonEmpty) {
+        val maxCount = partitionCountForStream.valuesIterator.max
+        val minCount = partitionCountForStream.valuesIterator.min
+        assertTrue("Scenario %s: assignment is not uniform (partition counts per stream are in the range [%d, %d])"
+          .format(scenario, minCount, maxCount), (maxCount - minCount) <= 1)
+      }
     }
   }