diff --git a/kyuubi-common/src/main/scala/org/apache/kyuubi/engine/result/TColumnGenerator.scala b/kyuubi-common/src/main/scala/org/apache/kyuubi/engine/result/TColumnGenerator.scala
index 7326e5a3d17..5a2acd0bdd7 100644
--- a/kyuubi-common/src/main/scala/org/apache/kyuubi/engine/result/TColumnGenerator.scala
+++ b/kyuubi-common/src/main/scala/org/apache/kyuubi/engine/result/TColumnGenerator.scala
@@ -34,18 +34,17 @@ trait TColumnGenerator[RowT] extends TRowSetColumnGetter[RowT] {
     val ret = new JArrayList[T](rowSize)
     val nulls = new JBitSet()
     var idx = 0
+    val isConvertFuncNull = convertFunc == null
     rows.foreach { row =>
-      val isNull = isColumnNullAt(row, ordinal)
-      if (isNull) {
+      val value = if (isColumnNullAt(row, ordinal)) {
         nulls.set(idx, true)
-        ret.add(defaultVal)
+        defaultVal
+      } else if (isConvertFuncNull) {
+        getColumnAs[T](row, ordinal)
       } else {
-        val value = Option(convertFunc) match {
-          case Some(f) => f(row, ordinal)
-          case _ => getColumnAs[T](row, ordinal)
-        }
-        ret.add(value)
+        convertFunc(row, ordinal)
       }
+      ret.add(value)
       idx += 1
     }
     (ret, ByteBuffer.wrap(nulls.toByteArray))