diff --git a/dibbler/models/Transaction.py b/dibbler/models/Transaction.py
index 863bd8e..0d6df69 100644
--- a/dibbler/models/Transaction.py
+++ b/dibbler/models/Transaction.py
@@ -83,8 +83,8 @@ def _transaction_type_field_constraints(
         or_(
             column("type") != transaction_type.value,
             and_(
-                *[column(field) != None for field in expected_fields],
-                *[column(field) == None for field in unexpected_fields],
+                *[column(field).is_not(None) for field in expected_fields],
+                *[column(field).is_(None) for field in unexpected_fields],
             ),
         ),
         name=f"trx_type_{transaction_type.value}_expected_fields",
diff --git a/dibbler/models/User.py b/dibbler/models/User.py
index 026c46a..8f7ca93 100644
--- a/dibbler/models/User.py
+++ b/dibbler/models/User.py
@@ -5,19 +5,14 @@ from typing import TYPE_CHECKING, Self
 from sqlalchemy import (
     Integer,
     String,
-    select,
 )
 from sqlalchemy.orm import (
     Mapped,
-    Session,
     mapped_column,
 )
 
 from .Base import Base
 
-if TYPE_CHECKING:
-    from .Transaction import Transaction
-
 
 class User(Base):
     id: Mapped[int] = mapped_column(Integer, primary_key=True)
diff --git a/dibbler/queries/__init__.py b/dibbler/queries/__init__.py
index 613b36b..417bf54 100644
--- a/dibbler/queries/__init__.py
+++ b/dibbler/queries/__init__.py
@@ -27,6 +27,7 @@ from .current_penalty import current_penalty
 from .joint_buy_product import joint_buy_product
 from .product_price import product_price, product_price_log
 from .product_stock import product_stock
+
 # from .products_owned_by_user import products_owned_by_user
 from .search_product import search_product
 from .search_user import search_user
diff --git a/dibbler/queries/transaction_log.py b/dibbler/queries/transaction_log.py
index bb552a7..998c210 100644
--- a/dibbler/queries/transaction_log.py
+++ b/dibbler/queries/transaction_log.py
@@ -13,15 +13,12 @@ def transaction_log(
     sql_session: Session,
     user: User | None = None,
     product: Product | None = None,
-
     exclusive_after: bool = False,
     after_time=None,
     after_transaction_id: int | None = None,
-
     exclusive_before: bool = False,
     before_time=None,
     before_transaction_id: int | None = None,
-
     transaction_type: list[TransactionType] | None = None,
     negate_transaction_type_filter: bool = False,
     limit: int | None = None,
diff --git a/dibbler/queries/user_balance.py b/dibbler/queries/user_balance.py
index f150f66..161502d 100644
--- a/dibbler/queries/user_balance.py
+++ b/dibbler/queries/user_balance.py
@@ -80,7 +80,6 @@ def _user_balance_query(
                             TransactionType.ADJUST_BALANCE,
                             TransactionType.BUY_PRODUCT,
                             TransactionType.TRANSFER,
-
                             # TODO: join this with the JOINT transactions, and determine
                             #       how much the current user paid for the product.
                             TransactionType.JOINT_BUY_PRODUCT,
diff --git a/dibbler/subcommands/transaction_log.py b/dibbler/subcommands/transaction_log.py
index 9629f0e..adc3080 100644
--- a/dibbler/subcommands/transaction_log.py
+++ b/dibbler/subcommands/transaction_log.py
@@ -2,6 +2,7 @@ from dibbler.db import Session
 from dibbler.queries import transaction_log
 from dibbler.lib.render_transaction_log import render_transaction_log
 
+
 def main() -> None:
     sql_session = Session()
 
diff --git a/tests/queries/test_product_price.py b/tests/queries/test_product_price.py
index 736fbe2..683ec24 100644
--- a/tests/queries/test_product_price.py
+++ b/tests/queries/test_product_price.py
@@ -386,7 +386,9 @@ def test_product_price_joint_transactions(sql_session: Session) -> None:
 
     old_product_price = product_price_
     product_price_ = product_price(sql_session, product)
-    assert product_price_ == old_product_price, "Joint buy transactions should not affect product price"
+    assert product_price_ == old_product_price, (
+        "Joint buy transactions should not affect product price"
+    )
 
     transactions = [
         Transaction.add_product(
diff --git a/tests/queries/test_product_stock.py b/tests/queries/test_product_stock.py
index e61c784..db03018 100644
--- a/tests/queries/test_product_stock.py
+++ b/tests/queries/test_product_stock.py
@@ -140,6 +140,7 @@ def test_negative_product_stock(sql_session: Session) -> None:
     # The stock should be negative because we added and bought the product
     assert product_stock(sql_session, product) == 1 - 2 - 1
 
+
 def test_product_stock_joint_transaction(sql_session: Session) -> None:
     insert_test_data(sql_session)