diff --git a/basicswap/db.py b/basicswap/db.py
index 5751673..1867c6e 100644
--- a/basicswap/db.py
+++ b/basicswap/db.py
@@ -966,8 +966,11 @@ class DBMethods:
                     query_data[cv_name] = cv
                 query += ") "
             else:
-                query += f" AND {ck} = :{ck} "
-                query_data[ck] = constraint_value
+                if constraint_value is None:
+                    query += f" AND {ck} IS NULL "
+                else:
+                    query += f" AND {ck} = :{ck} "
+                    query_data[ck] = constraint_value
 
         for order_col, order_dir in order_by.items():
             if validColumnName(order_col) is False:
diff --git a/tests/basicswap/test_xmr.py b/tests/basicswap/test_xmr.py
index e575ef1..4bde387 100644
--- a/tests/basicswap/test_xmr.py
+++ b/tests/basicswap/test_xmr.py
@@ -1137,12 +1137,10 @@ class Test(BaseTest):
         walletpath = os.path.join(
             chain_client_settings.get("datadir", "none"), "wallets", wallet_name
         )
-        wallet_cache_bytes = os.path.getsize(walletpath)
-        logging.info(f"[rm] wallet_cache_bytes {wallet_cache_bytes}")
-        logging.info(f"[rm] walletpath {walletpath}")
         shutil.copy(walletpath, walletpath + ".orig")
 
         # Failed to open wallet : basic_string::_M_replace_aux
+        # wallet_cache_bytes = os.path.getsize(walletpath)
         # with open(walletpath, "wb") as fp:
         #    fp.write(os.urandom(wallet_cache_bytes))