diff --git a/sky_phone/source/client/custom_apps.lua b/sky_phone/source/client/custom_apps.lua
index 87b4222..ea0ed2c 100644
--- a/sky_phone/source/client/custom_apps.lua
+++ b/sky_phone/source/client/custom_apps.lua
@@ -280,7 +280,8 @@ local function normalize_json_payload(payload, maximum_bytes)
         return nil, "payload_too_large"
     end
 
-    return json.decode(encoded)
+    local decoded = json.decode(encoded)
+    return decoded
 end
 
 local function validate_optional_text(value, error_code, maximum_length)
diff --git a/tests/custom_app_compat_client.lua b/tests/custom_app_compat_client.lua
index 558184d..09353b2 100644
--- a/tests/custom_app_compat_client.lua
+++ b/tests/custom_app_compat_client.lua
@@ -24,10 +24,16 @@ Config = {
 }
 
 json = {
-    decode = function()
+    decode = function(encoded)
+        if encoded == "null" then
+            return nil, 5
+        end
         return {}
     end,
-    encode = function()
+    encode = function(value)
+        if value == nil then
+            return "null"
+        end
         return "{}"
     end,
 }