diff --git a/dkb_robo/exemptionorder.py b/dkb_robo/exemptionorder.py
index e9b4fef..563559b 100644
--- a/dkb_robo/exemptionorder.py
+++ b/dkb_robo/exemptionorder.py
@@ -1,6 +1,6 @@
 """ Module for handling dkb standing orders """
-from typing import Dict, List
-from dataclasses import dataclass, field
+from typing import Dict, List, Optional
+from dataclasses import dataclass
 import logging
 import requests
 from dkb_robo.utilities import Amount, DKBRoboError, filter_unexpected_fields, object2dictionary
@@ -13,25 +13,28 @@
 @dataclass
 class PartnerItem:
     """ class for a single partner """
-    dateOfBirth: str = None
-    firstName: str = None
-    lastName: str = None
-    salutation: str = None
-    taxId: str = None
+    # pylint: disable=C0103
+    dateOfBirth: Optional[str] = None
+    firstName: Optional[str] = None
+    lastName: Optional[str] = None
+    salutation: Optional[str] = None
+    taxId: Optional[str] = None
 
 
 @filter_unexpected_fields
 @dataclass
 class ExemptionOrderItem:
     """ class for a single exemption order """
-    exemptionAmount: str = None
-    exemptionOrderType: str = None
-    partner: str = None
-    receivedAt: str = None
-    utilizedAmount: str = None
-    remainingAmount: str = None
-    validFrom: str = None
-    validUntil: str = None
+    # pylint: disable=C0103
+    exemptionAmount: Optional[str] = None
+    exemptionOrderType: Optional[str] = None
+    partner: Optional[str] = None
+    receivedAt: Optional[str] = None
+    utilizedAmount: Optional[str] = None
+    remainingAmount: Optional[str] = None
+    validFrom: Optional[str] = None
+    validUntil: Optional[str] = None
+
     def __post_init__(self):
         self.exemptionAmount = Amount(**self.exemptionAmount)
         self.remainingAmount = Amount(**self.remainingAmount)
diff --git a/dkb_robo/standingorder.py b/dkb_robo/standingorder.py
index 9bc2cbc..b9b18b8 100644
--- a/dkb_robo/standingorder.py
+++ b/dkb_robo/standingorder.py
@@ -13,28 +13,28 @@
 @dataclass
 class CreditorAccount:
     """ class for a single creditor account """
-    iban: str = None
-    bic: str = None
-    name: str = None
+    iban: Optional[str] = None
+    bic: Optional[str] = None
+    name: Optional[str] = None
 
 
 @filter_unexpected_fields
 @dataclass
 class DebtorAccount:
     """ class for a single debitor account """
-    iban: str = None
-    accountId: str = None  # pylint: disable=C0103 # NOSONAR
+    iban: Optional[str] = None
+    accountId: Optional[str] = None  # pylint: disable=C0103 # NOSONAR
 
 
 @filter_unexpected_fields
 @dataclass
 class Recurrence:
     """ class for frequency account """
-    frm: str = None
-    frequency: str = None
-    holidayExecutionStrategy: str = None  # pylint: disable=C0103 # NOSONAR
-    nextExecutionAt: str = None  # pylint: disable=C0103 # NOSONAR
-    until: str = None
+    frm: Optional[str] = None
+    frequency: Optional[str] = None
+    holidayExecutionStrategy: Optional[str] = None  # pylint: disable=C0103 # NOSONAR
+    nextExecutionAt: Optional[str] = None  # pylint: disable=C0103 # NOSONAR
+    until: Optional[str] = None
 
 
 @filter_unexpected_fields
@@ -44,10 +44,10 @@ class StandingOrderItem:
     amount: Optional[Amount] = None
     creditor: Optional[CreditorAccount] = None
     debtor: Optional[DebtorAccount] = None
-    description: str = None
+    description: Optional[str] = None
     messages: List[str] = field(default_factory=list)
     recurrence: Optional[Recurrence] = None
-    status: str = None
+    status: Optional[str] = None
 
     def __post_init__(self):
         self.amount = Amount(**self.amount)
diff --git a/dkb_robo/utilities.py b/dkb_robo/utilities.py
index 714b8a9..0697f71 100644
--- a/dkb_robo/utilities.py
+++ b/dkb_robo/utilities.py
@@ -26,6 +26,7 @@ def get_dateformat():
 @dataclass
 class Amount:
     """ Amount data class, roughly based on the JSON API response. """
+    # pylint: disable=c0103
     value: float = None
     currencyCode: str = None
 
@@ -94,13 +95,13 @@ def get_valid_filename(name):
         s = f'{generate_random_string(8)}.pdf'
     return s + p.suffix
 
-def object2dictionary(obj, key_lc=False, skip_list = []):
+
+def object2dictionary(obj, key_lc=False, skip_list=None):
     """ convert object to dict """
 
     output_dict = {}
-
     for k, v in asdict(obj).items():
-        if k in skip_list:
+        if isinstance(skip_list, list) and k in skip_list:
             continue
         if isinstance(v, dict):
             output_dict[k] = object2dictionary(v, key_lc=key_lc)