diff --git a/lib/xenu_nntp/db.py b/lib/xenu_nntp/db.py
index 1ae02ac..1502a15 100644
--- a/lib/xenu_nntp/db.py
+++ b/lib/xenu_nntp/db.py
@@ -3,6 +3,9 @@ import psycopg
 
 from xenu_nntp.config import Config
 
+def default(a, b):
+    return b if a is None else a
+
 class DatabaseOrder(enum.Enum):
     DEFAULT = 0
     ASC     = 1
@@ -145,13 +148,16 @@ class Database():
 
         self.db.execute(sql, values)
 
-    def query_sql(self, table, sql, values=list()):
+    def query_sql(self, table, sql, values: list=None):
         cr = DatabaseTableCursor(table, self.db.cursor())
-        cr.execute(sql, values)
+        cr.execute(sql, default(values, list()))
 
         return cr
 
-    def query(self, table, values=dict(), order_by=list()):
+    def query(self, table, values: dict=None, order_by: list=None):
+        values   = default(values,   dict())
+        order_by = default(order_by, list())
+
         sql = "select %s from %s" % (
             ', '.join(table.columns),
             table.name
@@ -181,10 +187,12 @@ class Database():
 
         return self.query_sql(table, sql, list(values.values()))
 
-    def get(self, table, values: dict=dict()):
-        return self.query(table, values).fetchone()
+    def get(self, table, values: dict=None):
+        return self.query(table, default(values, dict())).fetchone()
+
+    def _call(self, table, fn: str, column: str, values: dict=None) -> int:
+        values = default(values, dict())
 
-    def _call(self, table, fn: str, column: str, values: dict=dict()) -> int:
         sql = f"select {fn}({column}) as ret from {table.name}"
 
         if len(values) > 0:
@@ -195,11 +203,11 @@ class Database():
 
         return row[0] if row is not None else None
 
-    def min(self, table, column: str, values: dict=dict()) -> int:
-        return self._call(table, 'min', column, values)
+    def min(self, table, column: str, values: dict=None) -> int:
+        return self._call(table, 'min', column, default(values, dict()))
 
-    def max(self, table, column: str, values: dict=dict()) -> int:
-        return self._call(table, 'max', column, values)
+    def max(self, table, column: str, values: dict=None) -> int:
+        return self._call(table, 'max', column, default(values, dict()))
 
-    def count(self, table, values: dict=dict()) -> int:
-        return self._call(table, 'count', table.key, values)
+    def count(self, table, values: dict=None) -> int:
+        return self._call(table, 'count', table.key, default(values, dict()))