He'll swear the porter's upset about nothing! (7)

I believe the answer is:

trooper

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'he'll swear' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.

'porter's upset about nothing' is the wordplay.
'upset' indicates an anagram.
'about' means one lot of letters goes inside another.
'nothing' becomes 'O' (O resembles 0).
'porter' is an anagram of 'troper'.
'troper' enclosing 'o' is 'TROOPER'.

'the' acts as a link.

Can you help me to learn more?

(Other definitions for trooper that I've seen before include "ship" , "Proverbially swearing soldier" , "Cavalryman" , "Soldier, proverbial swearer" , "He swears" .)

I've seen this clue in the Evening Standard.

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