You can say someone without personality is: plain, dull, uninteresting, bland, vanilla (informal/slang/colloquial), or blah (also very informal). Slightly more advanced words to describe someone without personality are: insipid or vapid. Example: Your friend has a dull personality. He is very...vanilla.

You could say "He's a bore" or "He's got the personality of a moth"

Oh - it is so tempting to turn this into a joke/slur on some country. But then, this is not a very good website to do that...

can you explain more? what do you mean "without personality"?