dextend crashes on specific condition

[jdespatis]

Here is a code that make dextend crashes:

var dextend = require('deep-extend');

var left = {
    framework: {
        session: null
    }
};

var right = {
    framework: {
        session: { handler_id: null }
    }
};

dextend(left, right);

The error is:

./node_modules/deep-extend/index.js:55
                src = target[key];
                            ^
TypeError: Cannot read property 'handler_id' of null

Some missing initialization with { } I guess