fix: allow null values from --values to override parent chart values

Fixes #31919. Null values in override files now correctly remove parent chart defaults.

Made-with: Cursor

pkg/chart/common/util/coalesce.go

@@ -302,28 +302,20 @@ func coalesceTablesFullKey(printf printFn, dst, src map[string]any, prefix strin
 	if dst == nil {
 		return src
 	}
-	// Track original non-nil src keys before modifying src
-	// This lets us distinguish between user nullifying a chart default vs
-	// user setting nil for a key not in chart defaults.
-	srcOriginalNonNil := make(map[string]bool)
-	for key, val := range src {
-		if val != nil {
-			srcOriginalNonNil[key] = true
-		}
-	}
 	for key, val := range dst {
 		if val == nil {
-			src[key] = nil
+			if _, inSrc := src[key]; inSrc {
+				src[key] = nil
+			}
 		}
 	}
 	// Because dest has higher precedence than src, dest values override src
 	// values.
 	for key, val := range src {
 		fullkey := concatPrefix(prefix, key)
-		if dv, ok := dst[key]; ok && !merge && dv == nil && srcOriginalNonNil[key] {
-			// When coalescing (not merging), if dst has nil and src has a non-nil
-			// value, the user is nullifying a chart default - remove the key.
-			// But if src also has nil (or key not in src), preserve the nil
+		if dv, ok := dst[key]; ok && !merge && dv == nil {
+			// When coalescing (not merging), if dst has nil, remove the key.
+			// This allows null from --values to override and remove parent chart defaults.
 			delete(dst, key)
 		} else if !ok {
 			// key not in user values, preserve src value (including nil)