diff --git a/pallas-codec/src/utils.rs b/pallas-codec/src/utils.rs
index 864065d..8ce5005 100644
--- a/pallas-codec/src/utils.rs
+++ b/pallas-codec/src/utils.rs
@@ -574,3 +574,67 @@ impl<C, T> minicbor::Encode<C> for KeepRaw<'_, T> {
             .map_err(minicbor::encode::Error::write)
     }
 }
+
+#[derive(Clone, Debug)]
+pub enum Nullable<T> {
+    Some(T),
+    Null,
+    Undefined,
+}
+
+impl<'b, C, T> minicbor::Decode<'b, C> for Nullable<T>
+where
+    T: minicbor::Decode<'b, C>,
+{
+    fn decode(d: &mut minicbor::Decoder<'b>, ctx: &mut C) -> Result<Self, minicbor::decode::Error> {
+        match d.datatype()? {
+            minicbor::data::Type::Null => {
+                d.null()?;
+                Ok(Self::Null)
+            }
+            minicbor::data::Type::Undefined => {
+                d.undefined()?;
+                Ok(Self::Undefined)
+            }
+            _ => {
+                let x = d.decode_with(ctx)?;
+                Ok(Self::Some(x))
+            }
+        }
+    }
+}
+
+impl<C, T> minicbor::Encode<C> for Nullable<T>
+where
+    T: minicbor::Encode<C>,
+{
+    fn encode<W: minicbor::encode::Write>(
+        &self,
+        e: &mut minicbor::Encoder<W>,
+        ctx: &mut C,
+    ) -> Result<(), minicbor::encode::Error<W::Error>> {
+        match self {
+            Nullable::Some(x) => {
+                e.encode_with(x, ctx)?;
+                Ok(())
+            }
+            Nullable::Null => {
+                e.null()?;
+                Ok(())
+            }
+            Nullable::Undefined => {
+                e.undefined()?;
+                Ok(())
+            }
+        }
+    }
+}
+
+impl<T> From<Option<T>> for Nullable<T> {
+    fn from(x: Option<T>) -> Self {
+        match x {
+            Some(x) => Nullable::Some(x),
+            None => Nullable::Null,
+        }
+    }
+}
diff --git a/pallas-primitives/src/alonzo/model.rs b/pallas-primitives/src/alonzo/model.rs
index 4062af0..e7afcb2 100644
--- a/pallas-primitives/src/alonzo/model.rs
+++ b/pallas-primitives/src/alonzo/model.rs
@@ -5,7 +5,7 @@
 use pallas_codec::minicbor::{bytes::ByteVec, data::Int, data::Tag, Decode, Encode};
 use pallas_crypto::hash::Hash;
 
-use pallas_codec::utils::{AnyUInt, KeepRaw, KeyValuePairs, MaybeIndefArray};
+use pallas_codec::utils::{AnyUInt, KeepRaw, KeyValuePairs, MaybeIndefArray, Nullable};
 
 // required for derive attrs to work
 use pallas_codec::minicbor;
@@ -1373,7 +1373,7 @@ pub struct Tx {
     pub success: bool,
 
     #[n(3)]
-    pub auxiliary_data: Option<AuxiliaryData>,
+    pub auxiliary_data: Nullable<AuxiliaryData>,
 }
 
 #[derive(Encode, Decode, Debug, Clone)]
@@ -1388,7 +1388,7 @@ pub struct MintedTx<'b> {
     pub success: bool,
 
     #[n(3)]
-    pub auxiliary_data: Option<KeepRaw<'b, AuxiliaryData>>,
+    pub auxiliary_data: Nullable<KeepRaw<'b, AuxiliaryData>>,
 }
 
 #[cfg(test)]
diff --git a/pallas-primitives/src/babbage/model.rs b/pallas-primitives/src/babbage/model.rs
index 32cbb9f..612ef03 100644
--- a/pallas-primitives/src/babbage/model.rs
+++ b/pallas-primitives/src/babbage/model.rs
@@ -5,7 +5,7 @@
 use pallas_codec::minicbor::{bytes::ByteVec, Decode, Encode};
 use pallas_crypto::hash::Hash;
 
-use pallas_codec::utils::{CborWrap, KeepRaw, KeyValuePairs, MaybeIndefArray};
+use pallas_codec::utils::{CborWrap, KeepRaw, KeyValuePairs, MaybeIndefArray, Nullable};
 
 // required for derive attrs to work
 use pallas_codec::minicbor;
@@ -561,7 +561,7 @@ pub struct Tx {
     pub success: bool,
 
     #[n(3)]
-    pub auxiliary_data: Option<AuxiliaryData>,
+    pub auxiliary_data: Nullable<AuxiliaryData>,
 }
 
 #[derive(Encode, Decode, Debug, Clone)]
@@ -576,7 +576,7 @@ pub struct MintedTx<'b> {
     pub success: bool,
 
     #[n(3)]
-    pub auxiliary_data: Option<KeepRaw<'b, AuxiliaryData>>,
+    pub auxiliary_data: Nullable<KeepRaw<'b, AuxiliaryData>>,
 }
 
 #[cfg(test)]
diff --git a/pallas-traverse/src/support.rs b/pallas-traverse/src/support.rs
index 2c0b603..7907957 100644
--- a/pallas-traverse/src/support.rs
+++ b/pallas-traverse/src/support.rs
@@ -25,7 +25,8 @@ macro_rules! clone_tx_fn {
                         None
                     }
                 })
-                .cloned();
+                .cloned()
+                .into();
 
             let x = $era::MintedTx {
                 transaction_body,
diff --git a/pallas-traverse/src/tx.rs b/pallas-traverse/src/tx.rs
index 481ae4b..1af0667 100644
--- a/pallas-traverse/src/tx.rs
+++ b/pallas-traverse/src/tx.rs
@@ -219,8 +219,16 @@ impl<'b> MultiEraTx<'b> {
 
     fn aux_data(&self) -> Option<&KeepRaw<'_, AuxiliaryData>> {
         match self {
-            MultiEraTx::AlonzoCompatible(x, _) => x.auxiliary_data.as_ref(),
-            MultiEraTx::Babbage(x) => x.auxiliary_data.as_ref(),
+            MultiEraTx::AlonzoCompatible(x, _) => match &x.auxiliary_data {
+                pallas_codec::utils::Nullable::Some(x) => Some(x),
+                pallas_codec::utils::Nullable::Null => None,
+                pallas_codec::utils::Nullable::Undefined => None,
+            },
+            MultiEraTx::Babbage(x) => match &x.auxiliary_data {
+                pallas_codec::utils::Nullable::Some(x) => Some(x),
+                pallas_codec::utils::Nullable::Null => None,
+                pallas_codec::utils::Nullable::Undefined => None,
+            },
             MultiEraTx::Byron(_) => None,
         }
     }