diff --git a/ynab/models/hybrid_transaction.py b/ynab/models/hybrid_transaction.py
index b198820..9eeed32 100644
--- a/ynab/models/hybrid_transaction.py
+++ b/ynab/models/hybrid_transaction.py
@@ -6,7 +6,7 @@
     Our API uses a REST based design, leverages the JSON data format, and relies upon HTTPS for transport. We respond with meaningful HTTP response codes and if an error occurs, we include error details in the response body.  API Documentation is at https://api.youneedabudget.com  # noqa: E501
 
     OpenAPI spec version: 1.0.0
-    
+
     Generated by: https://github.com/swagger-api/swagger-codegen.git
 """
 
@@ -202,7 +202,7 @@ def memo(self, memo):
         :type: str
         """
         if memo is None:
-            raise ValueError("Invalid value for `memo`, must not be `None`")  # noqa: E501
+            memo = ""
 
         self._memo = memo
 
@@ -283,8 +283,9 @@ def flag_color(self, flag_color):
         :type: str
         """
         if flag_color is None:
-            raise ValueError("Invalid value for `flag_color`, must not be `None`")  # noqa: E501
-        allowed_values = ["red", "orange", "yellow", "green", "blue", "purple"]  # noqa: E501
+            flag_color = ""
+
+        allowed_values = ["red", "orange", "yellow", "green", "blue", "purple", ""]  # noqa: E501
         if flag_color not in allowed_values:
             raise ValueError(
                 "Invalid value for `flag_color` ({0}), must be one of {1}"  # noqa: E501
@@ -335,7 +336,7 @@ def payee_id(self, payee_id):
         :type: str
         """
         if payee_id is None:
-            raise ValueError("Invalid value for `payee_id`, must not be `None`")  # noqa: E501
+            payee_id = ""
 
         self._payee_id = payee_id
 
@@ -381,7 +382,8 @@ def transfer_account_id(self, transfer_account_id):
         :type: str
         """
         if transfer_account_id is None:
-            raise ValueError("Invalid value for `transfer_account_id`, must not be `None`")  # noqa: E501
+            transfer_account_id = ""
+
 
         self._transfer_account_id = transfer_account_id
 
@@ -406,7 +408,7 @@ def import_id(self, import_id):
         :type: str
         """
         if import_id is None:
-            raise ValueError("Invalid value for `import_id`, must not be `None`")  # noqa: E501
+            import_id = ""
 
         self._import_id = import_id
 
@@ -462,7 +464,7 @@ def parent_transaction_id(self, parent_transaction_id):
         :type: str
         """
         if parent_transaction_id is None:
-            raise ValueError("Invalid value for `parent_transaction_id`, must not be `None`")  # noqa: E501
+            parent_transaction_id = ""
 
         self._parent_transaction_id = parent_transaction_id
 
@@ -508,7 +510,7 @@ def payee_name(self, payee_name):
         :type: str
         """
         if payee_name is None:
-            raise ValueError("Invalid value for `payee_name`, must not be `None`")  # noqa: E501
+            payee_name = ""
 
         self._payee_name = payee_name
 
@@ -531,7 +533,7 @@ def category_name(self, category_name):
         :type: str
         """
         if category_name is None:
-            raise ValueError("Invalid value for `category_name`, must not be `None`")  # noqa: E501
+            category_name = ""
 
         self._category_name = category_name
 
diff --git a/ynab/models/sub_transaction.py b/ynab/models/sub_transaction.py
index 80ced1e..65fc011 100644
--- a/ynab/models/sub_transaction.py
+++ b/ynab/models/sub_transaction.py
@@ -6,7 +6,7 @@
     Our API uses a REST based design, leverages the JSON data format, and relies upon HTTPS for transport. We respond with meaningful HTTP response codes and if an error occurs, we include error details in the response body.  API Documentation is at https://api.youneedabudget.com  # noqa: E501
 
     OpenAPI spec version: 1.0.0
-    
+
     Generated by: https://github.com/swagger-api/swagger-codegen.git
 """
 
@@ -160,7 +160,7 @@ def memo(self, memo):
         :type: str
         """
         if memo is None:
-            raise ValueError("Invalid value for `memo`, must not be `None`")  # noqa: E501
+            memo = ''
 
         self._memo = memo