Replaces a UUID that has been saved as BinData(0, "") as a UUID.

mongodb-fix-uuid-0

function decode_base64(s) {
    var e={},i,k,v=[],r='',w=String.fromCharCode;
    var n=[[65,91],[97,123],[48,58],[43,44],[47,48]];

    for(z in n){for(i=n[z][0];i<n[z][1];i++){v.push(w(i));}}
    for(i=0;i<64;i++){e[v[i]]=i;}

    for(i=0;i<s.length;i+=72){
        var b=0,c,x,l=0,o=s.substring(i,i+72);
        for(x=0;x<o.length;x++){
            c=e[o.charAt(x)];b=(b<<6)+c;l+=6;
            while(l>=8){r+=w((b>>>(l-=8))%256);}
        }
    }
    return r;
}

db.myDatabase.find(function() { return this.myUuidField.subtype() == 3 }).snapshot().forEach(function(elem) {
        db.myDatabase.update(
            {
                _id: elem._id
            },
            {
                $set: {
                    myUuidField: UUID(decode_base64(elem.myUuidField.base64()).replace(/-/gi, ''))
                }
            }
        )
})