Key Not Found exception when I try to use my custom Transformer

Hi Team, I am trying to use MLeap to bundle my spark ML pipeline and I am using spark ML inbuild as well as custom transformers in the pipeline. It throws exception on bundle serialization. I am not sure if MLeap doesn't support custom transformer or if its some other issue. I am using spark 3.0.1 and Mleap-spark 0.16.0 , can you please advise? Really appreciate your help!

Exception in thread "main" java.util.NoSuchElementException: key not found: my_custom_transfomer
at scala.collection.MapLike.default(MapLike.scala:235)
at scala.collection.MapLike.default$(MapLike.scala:234)
at scala.collection.AbstractMap.default(Map.scala:65)
at scala.collection.MapLike.apply(MapLike.scala:144)
at scala.collection.MapLike.apply$(MapLike.scala:143)
at scala.collection.AbstractMap.apply(Map.scala:65)
at ml.combust.bundle.BundleRegistry.opForObj(BundleRegistry.scala:102)
at ml.combust.bundle.serializer.GraphSerializer.$anonfun$writeNode$1(GraphSerializer.scala:31)
at scala.util.Try$.apply(Try.scala:213)
at ml.combust.bundle.serializer.GraphSerializer.writeNode(GraphSerializer.scala:30)
at ml.combust.bundle.serializer.GraphSerializer.$anonfun$write$2(GraphSerializer.scala:21)
at scala.collection.IndexedSeqOptimized.foldLeft(IndexedSeqOptimized.scala:60)
at scala.collection.IndexedSeqOptimized.foldLeft$(IndexedSeqOptimized.scala:68)
at scala.collection.mutable.WrappedArray.foldLeft(WrappedArray.scala:38)
at ml.combust.bundle.serializer.GraphSerializer.write(GraphSerializer.scala:21)
at org.apache.spark.ml.bundle.ops.PipelineOp$$anon$1.store(PipelineOp.scala:21)
at org.apache.spark.ml.bundle.ops.PipelineOp$$anon$1.store(PipelineOp.scala:14)
at ml.combust.bundle.serializer.ModelSerializer.$anonfun$write$1(ModelSerializer.scala:87)
at scala.util.Try$.apply(Try.scala:213)
at ml.combust.bundle.serializer.ModelSerializer.write(ModelSerializer.scala:83)
at ml.combust.bundle.serializer.NodeSerializer.$anonfun$write$1(NodeSerializer.scala:85)
at scala.util.Try$.apply(Try.scala:213)
at ml.combust.bundle.serializer.NodeSerializer.write(NodeSerializer.scala:81)
at ml.combust.bundle.serializer.BundleSerializer.$anonfun$write$1(BundleSerializer.scala:34)
at scala.util.Try$.apply(Try.scala:213)
at ml.combust.bundle.serializer.BundleSerializer.write(BundleSerializer.scala:29)
at ml.combust.bundle.BundleWriter.save(BundleWriter.scala:34)