Verifying if a specific data portion is part of a tree

Can someone help me here ...

I tried the example provided with merkle-lib and it works correctly.

But if I try to create a new buffer data with the same string and use the library to check if it is included in the library it end up with a no proof result .

For example while using

var proof = merkleProof(tree,new Buffer('bbbbbbbb', 'hex'))
Instead of:
var proof = merkleProof(tree, data[0])
In example provided

Regards