Why is this an issue?

The Duplicates property on TStringList has no effect unless the list is sorted, so setting Duplicates on an unsorted list is either an unnecessary line of code or a bug.

Note that for the purposes of this rule, the list must be sorted in the same block where Duplicates is set.

How to fix it

If the list should be forbidding duplicates, sort the list:

procedure DoSomething(MyList: TStringList);
begin
  MyList.Duplicates := dupError;
  // ...
end;

procedure DoSomething(MyList: TStringList);
begin
  MyList.Sorted := True;
  MyList.Duplicates := dupError;
  // ...
end;

If the list should not be forbidding duplicates, remove the assignment:

procedure DoSomething(MyList: TStringList);
begin
  MyList.Duplicates := dupError;
  // ...
end;

procedure DoSomething(MyList: TStringList);
begin
  // ...
end;

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