Fix typo in example

articles/20241114-til-counting-nulls-in-postgres.md

@@ -28,8 +28,8 @@ This is useful in a check constraint, if you need to ensure that exactly some nu
 ```sql
 CREATE TABLE purchase_order (
     id UUID PRIMARY KEY,
-    contact_email TEXT NULLABLE,
-    contact_phone TEXT NULLABLE
+    contact_email TEXT NULL,
+    contact_phone TEXT NULL
 );
 
 -- If we want to ensure that at least one of email or phone is provided 
@@ -40,4 +40,4 @@ ALTER TABLE purchase_order ADD CONSTRAINT contact_info_check CHECK (
 );
 ```
 
-`num_nonnulls` and `num_nulls` are available in Postgres 9.6+ ([docs](https://www.postgresql.org/docs/9.6/functions-comparison.html#:~:text=Table%209%2D3.%20Comparison%20Functions))
+`num_nonnulls` and `num_nulls` are available in Postgres 9.6+ ([docs](https://www.postgresql.org/docs/9.6/functions-comparison.html#:~:text=Table%209%2D3.%20Comparison%20Functions))