Adding to a dictionary and skipping duplicate keys

What is the cleanest way to use dictionaries and protect against an unhandled ArgumentException if the key already exists in the dictionary?

I'd like to say that I can always guarantee uniqueness upstream, but I'm dealing with legacy code and mildly corrupt data from an old bug in the system.

I find myself using this pattern frequently but wonder if there is a better way.

public void AddToDictionaryContainsKey(Dictionary myDictionary, int myKey, string myValue )
{
    if (!myDictionary.ContainsKey(myKey))
    {
        myDictionary.Add(myKey, myValue);
    }
}

Maybe a try/catch block - but this seems less readable. The advantage is that if I ever do decide to log the problem I have a place to do it.

public void AddToDictionaryTryCatch(Dictionary myDictionary, int myKey, string myValue)
{
    try
    {
        myDictionary.Add(myKey, myValue);
    }
    catch (ArgumentException e)
    {
        // keep on truckin'
    }
}

The dictionaries are relatively small (typically < 1000 entries) so I prefer readability over performance.

Generating and handling exceptions is considered to be an expensive operation, so if(! x.ContainsKey()) is better. Yeah, the code example I see in MSDN uses try/catch but that's to illustrate the exception not advocate that as "best practice." Documentation I've read is pretty adamant about not throwing exceptions needlessly.

And you don't need try/catch to trap the duplicate key; just an else to the above if.

StackExchange Code Review Q#124309, answer score: 15