OneHotEncoder serialization failed

To who it may concern,

I'm using mleap-pyspark to serialize the following pipeline using pyspark 3.0.2 and mleap 0.18.1.

imputer --> string_indexer --> imputer --> string_indexer --> one_hot_encoder --> vector_assembler --> scaler --> vector_assembler --> random_classifier

But I get this error:

`
Py4JJavaError: An error occurred while calling o99817.serializeToBundle. : java.lang.RuntimeException: unsupported attribute for field loan_term_idx_imputed at org.apache.spark.ml.bundle.ops.feature.OneHotEncoderOp$.sizeForField(OneHotEncoderOp.scala:31) at org.apache.spark.ml.bundle.ops.feature.OneHotEncoderOp$$anon$1.$anonfun$store$2(OneHotEncoderOp.scala:47) at org.apache.spark.ml.bundle.ops.feature.OneHotEncoderOp$$anon$1.$anonfun$store$2$adapted(OneHotEncoderOp.scala:47) at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:238) at scala.collection.IndexedSeqOptimized.foreach(IndexedSeqOptimized.scala:36) at scala.collection.IndexedSeqOptimized.foreach$(IndexedSeqOptimized.scala:33) at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:198) at scala.collection.TraversableLike.map(TraversableLike.scala:238) at scala.collection.TraversableLike.map$(TraversableLike.scala:231) at scala.collection.mutable.ArrayOps$ofRef.map(ArrayOps.scala:198) at org.apache.spark.ml.bundle.ops.feature.OneHotEncoderOp$$anon$1.store(OneHotEncoderOp.scala:47) at org.apache.spark.ml.bundle.ops.feature.OneHotEncoderOp$$anon$1.store(OneHotEncoderOp.scala:37) at ml.combust.bundle.serializer.ModelSerializer.$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.GraphSerializer.$anonfun$writeNode$1(GraphSerializer.scala:34) at scala.util.Try$.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) at ml.combust.mleap.spark.SimpleSparkSerializer.$anonfun$serializeToBundleWithFormat$4(SimpleSparkSerializer.scala:26) at resource.AbstractManagedResource.$anonfun$acquireFor$1(AbstractManagedResource.scala:88) at scala.util.control.Exception$Catch.$anonfun$either$1(Exception.scala:252) at scala.util.control.Exception$Catch.apply(Exception.scala:228) at scala.util.control.Exception$Catch.either(Exception.scala:252) at resource.AbstractManagedResource.acquireFor(AbstractManagedResource.scala:88) at resource.ManagedResourceOperations.apply(ManagedResourceOperations.scala:26) at resource.ManagedResourceOperations.apply$(ManagedResourceOperations.scala:26) at resource.AbstractManagedResource.apply(AbstractManagedResource.scala:50) at resource.DeferredExtractableManagedResource.$anonfun$tried$1(AbstractManagedResource.scala:33) at scala.util.Try$.apply(Try.scala:213) at resource.DeferredExtractableManagedResource.tried(AbstractManagedResource.scala:33) at ml.combust.mleap.spark.SimpleSparkSerializer.serializeToBundleWithFormat(SimpleSparkSerializer.scala:25) at ml.combust.mleap.spark.SimpleSparkSerializer.serializeToBundle(SimpleSparkSerializer.scala:17) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at py4j.reflection.MethodInvoker.invoke(MethodInvoker.java:244) at py4j.reflection.ReflectionEngine.invoke(ReflectionEngine.java:357) at py4j.Gateway.invoke(Gateway.java:282) at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:132) at py4j.commands.CallCommand.execute(CallCommand.java:79) at py4j.GatewayConnection.run(GatewayConnection.java:238) at java.lang.Thread.run(Thread.java:748)
`

Any insights?