It's redundancy calls because pop should already removed the element.

samnang · samnang · commit 2eeb2646db9c · 2023-07-18T20:46:48.000+07:00
diff --git a/contracts/sample_apps/02_address_book/AddressBook.sol b/contracts/sample_apps/02_address_book/AddressBook.sol
@@ -29,7 +29,6 @@ contract AddressBook {
                     contacts[msg.sender][i] = contacts[msg.sender][length - 1];
                 }
 
-                delete contacts[msg.sender][length - 1];
                 contacts[msg.sender].pop();
 
                 delete aliases[msg.sender][contactAddress];

Original file line number	Diff line number	Diff line change
`@@ -29,7 +29,6 @@ contract AddressBook {`
`29`	`29`	`contacts[msg.sender][i] = contacts[msg.sender][length - 1];`
`30`	`30`	`}`
`31`	`31`
`32`		`- delete contacts[msg.sender][length - 1];`
`33`	`32`	`contacts[msg.sender].pop();`
`34`	`33`
`35`	`34`	`delete aliases[msg.sender][contactAddress];`