Fix many nested records failing to save

This happened when new many nested record on an update form was
deleted on the form, and the form was finally submitted.

Author: akadusei

CHANGELOG.md

@@ -5,6 +5,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## [Unreleased] - 
+
+### Fixed
+- Fix new many nested records failing to save when they were deleted on the form before form submission
+
 ## [0.21.3] - 2025-08-30
 
 ### Fixed

src/bill/operations/mixins/needs_line_items.cr

@@ -32,7 +32,7 @@ module Bill::NeedsLineItems
     end
 
     def line_items_to_delete
-      keyed_line_items - line_items_to_save
+      (keyed_line_items - line_items_to_save).select(&.["id"]?.presence)
     end
 
     def line_items_to_save