Delete / F/K error

I tried to delete a row from 'sites' and get this
rather complex error:

SQL error:

ERROR: insert or update on table "types" violates
foreign key constraint "$1"
DETAIL: Key (page_template_id)=(8) is not present in
table "templates".
CONTEXT: SQL statement "UPDATE ONLY "public"."types"
SET "item_template_id" = NULL WHERE "item_template_id"
= $1"
SQL statement "DELETE FROM ONLY "public"."templates"
WHERE "site_id" = $1"

In statement:
DELETE FROM "sites" WHERE "id"='1'

I'm not sure what's wrong, or how to fix it. Any
ideas?

thanks
csn

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