nasty error message

[maxogden]

calling this https://github.com/maxogden/dat/blob/c29fe52378fcdd025c6b664f6fc371b0592e2a6b/index.js#L128

on an entry that has no data (in this case it is a folder that was added as a type: file) causes this error stack:

buffer.js:572
        return this.utf8Write(string, offset, length);
                    ^

TypeError: Argument must be a string
    at TypeError (native)
    at Buffer.write (buffer.js:572:21)
    at Object.exports.bytes.encode (/Users/max/src/js/dat/node_modules/hyperdrive/node_modules/protocol-buffers/encodings.js:35:17)
    at Object.encode (eval at <anonymous> (/Users/max/src/js/dat/node_modules/hyperdrive/node_modules/protocol-buffers/node_modules/generate-function/index.js:55:21), <anonymous>:13:10)
    at Protocol._push (/Users/max/src/js/dat/node_modules/hyperdrive/lib/protocol.js:290:7)
    at Protocol.join (/Users/max/src/js/dat/node_modules/hyperdrive/lib/protocol.js:302:8)
    at Swarm.join (/Users/max/src/js/dat/node_modules/hyperdrive/lib/swarm.js:135:19)
    at new Feed (/Users/max/src/js/dat/node_modules/hyperdrive/lib/feed.js:24:37)
    at Feed (/Users/max/src/js/dat/node_modules/hyperdrive/lib/feed.js:11:39)
    at Hyperdrive.get (/Users/max/src/js/dat/node_modules/hyperdrive/index.js:42:10)

would be nice to have a more user friendly error here