Compiler warning "return value might be undefined"

I often use code along the lines of:

function GetNumber(Handle : THandle) : Integer;
begin
FLock.BeginRead;
try
  if FMap.TryGetValue(Handle, Object) then
    raise EArgumentException.Create('Invalid handle');
  Result := Object.Number;
finally
  FLock.EndRead;
end;
end;

Unfortunately the compiler gives me a warning for all these methods:

[DCC Warning] Unit.pas(1012): W1035 Return value of function 'GetNumber' might be undefined

I know this warning, but in this case I can't see any reason for it at all. Or is there a scenario that I am missing that would result in an undefined result value? I understand the warning in the case of try..except but for try..finally it does not make sense to me.

Questions:

• Is there any reason for the warning?
• How can I get rid of it (moving the Result := Object.Number line out of the lock is not an option, and I want to avoid writing an completely unnecessary Result := 0 line at the top of each function)

Thanks!