I might be missing something, but it depends what you DO want in the cells E4 and E5. probably telling you what you already know, but whatever is between the speechmarks in the formula for the "false" argument is what will appear in the cell. So if you wanted for example the word null to appear in that range if it wasn't the client, you'd simply put "null" in place of ""

That said, if you're looking to do one persons credit account, why would you have other peoples data in the sheet? And if you do need a range of data, then certainly filter seems a good option....