remove null requirement on agreement content

src/db/migrations/000009 - null-user-agreement.sql

@@ -0,0 +1,11 @@
+DO $$ BEGIN
+IF EXISTS (
+    SELECT 1
+    FROM information_schema.columns
+    WHERE table_name = 'agreement'
+        AND column_name = 'user_id'
+        AND is_nullable = 'NO'
+) THEN
+    EXECUTE 'ALTER TABLE agreement ALTER COLUMN user_id DROP NOT NULL';
+END IF;
+END $$;