From 0043d73ae3bf392807a911670c6e2421353d5186 Mon Sep 17 00:00:00 2001
From: Mario Buikhuizen <mariobuikhuizen@widgetti.io>
Date: Fri, 1 Sep 2023 14:52:03 +0200
Subject: [PATCH 1/2] test: add test for use_thread on memoize returning None
 after hit

---
 tests/unit/cache_test.py | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/tests/unit/cache_test.py b/tests/unit/cache_test.py
index 295d3dddf..ca28c67c0 100644
--- a/tests/unit/cache_test.py
+++ b/tests/unit/cache_test.py
@@ -252,3 +252,41 @@ def f(x: int) -> int:
     # we should directly get the result from the cache, so we don't go into running state
     assert result_values[0].state == solara.ResultState.FINISHED
     assert result_values[0].value == 100
+
+
+def test_memoize_hook_no_None_after_hit():
+    has_been_none = False
+
+    selected = solara.Reactive("1")
+
+    @solara.memoize
+    def something(i):
+        return i
+
+    @solara.component
+    def Test():
+        result = something.use_thread(selected.value)
+
+        if result.state == solara.ResultState.FINISHED:
+            if result.value is None:
+                # this should not happen
+                nonlocal has_been_none
+                has_been_none = True
+
+            solara.Text(str(result.value))
+
+    box, rc = solara.render(Test(), handle_error=False)
+    rc.find(v.Html, children=["1"]).wait_for(timeout=2)
+
+    assert not has_been_none
+    selected.set("2")
+    rc.find(v.Html, children=["2"]).wait_for(timeout=2)
+    assert not has_been_none
+
+    selected.set("1")
+    rc.find(v.Html, children=["1"]).wait_for(timeout=2)
+    assert not has_been_none
+
+    selected.set("3")
+    rc.find(v.Html, children=["3"]).wait_for(timeout=2)
+    assert not has_been_none

From 9474620376dbc892d124ff00919c23ba79c31014 Mon Sep 17 00:00:00 2001
From: Mario Buikhuizen <mariobuikhuizen@widgetti.io>
Date: Fri, 1 Sep 2023 15:11:32 +0200
Subject: [PATCH 2/2] fix: use_thread on memoize returning None after hit

---
 solara/cache.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/solara/cache.py b/solara/cache.py
index 9bf582ab5..60585d8c1 100644
--- a/solara/cache.py
+++ b/solara/cache.py
@@ -128,8 +128,9 @@ def do_work():
                 self.storage[key] = new_value
                 return new_value
             else:
-                # we don't use the return value if value is _DOES_NOT_EXIST
-                return None
+                # although we don't use the return value directly, it's still used on the next time result_thread is
+                # returned.
+                return value
 
         result_thread: solara.Result[R] = solara.use_thread(do_work, dependencies=[key], intrusive_cancel=self.intrusive_cancel)
         if value is _DOES_NOT_EXIST: