chore: make empty files cause the same cid as go

Author: achingbrain

src/index.js

@@ -73,15 +73,23 @@ function Data (type, data) {
     }
     let fileSize = this.fileSize()
 
-    if (!fileSize) {
-      fileSize = undefined
+    let data = this.data
+
+    if (!this.data || !this.data.length) {
+      data = undefined
+    }
+
+    let blockSizes = this.blockSizes
+
+    if (!this.blockSizes || !this.blockSizes.length) {
+      blockSizes = undefined
     }
 
     return unixfsData.encode({
       Type: type,
-      Data: this.data,
+      Data: data,
       filesize: fileSize,
-      blocksizes: this.blockSizes.length > 0 ? this.blockSizes : undefined,
+      blocksizes: blockSizes,
       hashType: this.hashType,
       fanout: this.fanout
     })

test/unixfs-format.spec.js

@@ -135,4 +135,11 @@ describe('unixfs-format', () => {
       // expect(unmarshalled.marshal()).to.deep.equal(symlink)
     })
   })
+
+  it('empty', () => {
+    const data = new UnixFS('file')
+    const marshalled = data.marshal()
+
+    expect(marshalled).to.deep.equal(Buffer.from([0x08, 0x02, 0x18, 0x00]))
+  })
 })