feat: coerce undefined to null on decode

Fixes: #44
Ref: ipld/go-ipld-prime#308

index.js

@@ -85,7 +85,7 @@ function cidDecoder (bytes) {
 
 const decodeOptions = {
   allowIndefinite: false,
-  allowUndefined: false,
+  allowUndefined: true,
   allowNaN: false,
   allowInfinity: false,
   allowBigInt: true, // this will lead to BigInt for ints outside of

test/test-basics.js

@@ -79,12 +79,6 @@ describe('dag-cbor', () => {
     assert.throws(() => encode(objWithUndefined), /\Wundefined\W.*not supported/)
   })
 
-  test('error on decoding undefined', () => {
-    // encoded forms from the encode() test above
-    assert.throws(() => decode(bytes.fromHex('f7')), /\Wundefined\W.*not supported/)
-    assert.throws(() => decode(bytes.fromHex('a2616161616162f7')), /\Wundefined\W.*not supported/)
-  })
-
   test('error on encoding IEEE 754 specials', () => {
     for (const special of [NaN, Infinity, -Infinity]) {
       assert.throws(() => encode(special), new RegExp(`\\W${String(special)}\\W.*not supported`))
@@ -169,4 +163,15 @@ describe('dag-cbor', () => {
     const encoded = bytes.fromHex('a1646c696e6bd82a582501017012207252523e6591fb8fe553d67ff55a86f84044b46a3e4176e10c58fa529a4aabd5')
     assert.throws(() => decode(encoded), /Invalid CID for CBOR tag 42; expected leading 0x00/)
   })
+
+  test('sloppy decode: coerce undefined', () => {
+    // See https://github.com/ipld/js-dag-cbor/issues/44 for context on this
+    let encoded = bytes.fromHex('f7')
+    let decoded = decode(encoded)
+    same(null, decoded)
+
+    encoded = bytes.fromHex('a26362617af763666f6f63626172')
+    decoded = decode(encoded)
+    same({ foo: 'bar', baz: null }, decoded)
+  })
 })