fix(schema): schema validation to handle potential nil field case (#…

…13861)

Adjusted schema validation logic to account for `nil` field scenario, 
ensuring proper handling of fields to prevent errors.

Fix:[FTI-6336](https://konghq.atlassian.net/browse/FTI-6336)

---------

Signed-off-by: tzssangglass <tzssangglass@gmail.com>
Co-authored-by: Keery Nie <windmgc@gmail.com>

changelog/unreleased/kong/fix-schema-validation-with-nil-field.yml

@@ -0,0 +1,3 @@
+message: "Fixed a 500 error triggered by unhandled nil fields during schema validation."
+type: bugfix
+scope: Core

kong/db/schema/init.lua

@@ -1273,7 +1273,7 @@ local function run_entity_check(self, name, input, arg, full_check, errors)
 
       -- Don't run if any of the values is a reference in a referenceable field
       local field = get_schema_field(self, fname)
-      if field.type == "string" and field.referenceable and is_reference(value) then
+      if field and field.type == "string" and field.referenceable and is_reference(value) then
         return
       end
     end

spec/01-unit/01-db/01-schema/06-routes_spec.lua

@@ -1800,3 +1800,34 @@ describe("routes schema (flavor = expressions)", function()
     end
   end)
 end)
+
+
+describe("routes schema (flavor = traditional_compatible)", function()
+  local a_valid_uuid = "cbb297c0-a956-486d-ad1d-f9b42df9465a"
+  local another_uuid = "64a8670b-900f-44e7-a900-6ec7ef5aa4d3"
+
+  reload_flavor("traditional_compatible")
+  setup_global_env()
+
+  it("validates a route with only expression field", function()
+    local route = {
+      id             = a_valid_uuid,
+      name           = "my_route",
+      protocols      = { "http" },
+      hosts           = { "example.com" },
+      expression     = [[(http.method == "GET")]],
+      priority       = 100,
+      service        = { id = another_uuid },
+    }
+    route = Routes:process_auto_fields(route, "insert")
+    assert.truthy(route.created_at)
+    assert.truthy(route.updated_at)
+    assert.same(route.created_at, route.updated_at)
+    local ok, errs = Routes:validate(route)
+    assert.falsy(ok)
+    assert.same({
+      ["expression"] = 'unknown field',
+      ["priority"] = 'unknown field'
+    }, errs)
+  end)
+end)