check if multiple text boxes are empty

What I need is some code to check if a few text boxes are empty, if the text box is empty then a message box should pop up that displays all which text boxes are empty and afterwards aborts the rest of the code.

example:

Company name: (Blank)
Brand name: (Blank)
cost: (Blank)

after hitting submit a text box should pop up and inform the user that the above data is missing and stop the rest of the code from executing.

below is the code I have however it does not stop the data that eventually gets added from being added to the spreadsheet

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rest of the code

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Hello,

Probley not the prittiest way of going about it though it should work.

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hope it helps