fix: Improve error for tag resolution error on null value (#616)

Author: eemeli

src/stringify/stringify.ts

@@ -109,7 +109,8 @@ function getTagObject(tags: Array<ScalarTag | CollectionTag>, item: Node) {
   }
 
   if (!tagObj) {
-    const name = (obj as any)?.constructor?.name ?? typeof obj
+    const name =
+      (obj as any)?.constructor?.name ?? (obj === null ? 'null' : typeof obj)
     throw new Error(`Tag not resolved for ${name} value`)
   }
   return tagObj

tests/doc/types.ts

@@ -1225,6 +1225,12 @@ describe('schema changes', () => {
     expect(() => String(doc)).toThrow(/Tag not resolved for Date value/)
   })
 
+  test('fail for missing null type (#616)', () => {
+    const doc = parseDocument('foo:')
+    doc.setSchema('1.2', { schema: 'failsafe' })
+    expect(() => String(doc)).toThrow(/Tag not resolved for null value/)
+  })
+
   test('set schema + custom tags', () => {
     const doc = parseDocument('foo: 1971-02-03T12:13:14', {
       version: '1.1'