Bugfix ensure None is returned if there is no result

Without this fix the code would instead raise an exception
incorrectly.

src/quart_db/backends/aiosqlite.py

@@ -113,29 +113,33 @@ async def fetch_one(
         self,
         query: LiteralString,
         values: Optional[Dict[str, Any]] = None,
-    ) -> RecordType:
+    ) -> Optional[RecordType]:
         try:
             async with self._lock:
                 async with self._connection.execute(query, values) as cursor:
                     row = await cursor.fetchone()
         except ProgrammingError as error:
             raise UndefinedParameterError(str(error))
         else:
-            return {key: row[key] for key in row.keys()}
+            if row is not None:
+                return {key: row[key] for key in row.keys()}
+            return None
 
     async def fetch_val(
         self,
         query: LiteralString,
         values: Optional[Dict[str, Any]] = None,
-    ) -> Any:
+    ) -> Optional[Any]:
         try:
             async with self._lock:
                 async with self._connection.execute(query, values) as cursor:
                     result = await cursor.fetchone()
         except ProgrammingError as error:
             raise UndefinedParameterError(str(error))
         else:
-            return result[0]
+            if result is not None:
+                return result[0]
+            return None
 
     async def iterate(
         self,

src/quart_db/interfaces.py

@@ -89,7 +89,9 @@ async def fetch_one(
         pass
 
     @abstractmethod
-    async def fetch_val(self, query: LiteralString, values: Optional[Dict[str, Any]] = None) -> Any:
+    async def fetch_val(
+        self, query: LiteralString, values: Optional[Dict[str, Any]] = None
+    ) -> Optional[Any]:
         """Execute a query, returning only a value
 
         The query accepts named arguments i.e. `:name`in the query

tests/test_connection.py

@@ -25,11 +25,21 @@ async def test_fetch_one(connection: Connection) -> None:
     assert result["data"] == 2
 
 
+async def test_fetch_one_no_result(connection: Connection) -> None:
+    result = await connection.fetch_one("SELECT * FROM tbl WHERE id = -1")
+    assert result is None
+
+
 async def test_fetch_val(connection: Connection) -> None:
     value = await connection.fetch_val("SELECT 2")
     assert value == 2
 
 
+async def test_fetch_val_no_result(connection: Connection) -> None:
+    value = await connection.fetch_val("SELECT id FROM tbl WHERE id = -1")
+    assert value is None
+
+
 async def test_iterate(connection: Connection) -> None:
     await connection.execute_many(
         "INSERT INTO tbl (data) VALUES (:data)",