Postgres UPDATE numeric field to NULL failing

I've built this query:

UPDATE opportunity o
SET updated = NOW(), updated_user_id = {{ user_id }},
  status_id = {{ status_id }},
  array_size = {{ array_size == "" ? "NULL" : array_size }}
WHERE id = {{ opp_id }};

If array_size is empty ("") in my app, I want it to update the value of array_size (decimal(5,1)) to NULL.
Here's an example of my query's .query property value (i.e. the generated SQL):

UPDATE opportunity o
SET updated = NOW(), updated_user_id = 19,
  status_id = 587,
  array_size = NULL
WHERE id = 12257;

This SQL runs just fine if I execute it manually against my db.

When Retool executes it I get this error:
invalid input syntax for type numeric: "NULL"

I've tried many different approaches to try and get around this and none of them have worked.

Can you help me solve this problem?

Thank you,
Rob

This is against a Postgres db.

Solved.
I disabled Prepared Statement creation on my Postgres resource.