support null value include in @Scopes

[hiradimir]

I got error of below log and fixed it.
This error occurred by null value in @Scopes.

/home/user/app/node_modules/sequelize-typescript/lib/utils/object.js:10
            .getOwnPropertyNames(source)
             ^
TypeError: Cannot convert undefined or null to object
    at Function.getOwnPropertyNames (<anonymous>)
    at /home/user/app/node_modules/sequelize-typescript/lib/utils/object.js:10:14
    at Array.forEach (native)
    at deepAssign (/home/user/app/node_modules/sequelize-typescript/lib/utils/object.js:8:13)
    at assign (/home/user/app/node_modules/sequelize-typescript/lib/utils/object.js:34:21)
    at /home/user/app/node_modules/sequelize-typescript/lib/utils/object.js:11:46
    at Array.forEach (native)

[hiradimir]

above L39 condition of
} else if (typeof sourceValue === 'object') {
is true if sourceValue = null.

---

and null value is occurring exception with below else sesion deepAssign

[RobinBuschmann]

Thank you - looks good :)