remove redundant dictionary lookups

[SimonCropp]

No description provided.

[paulushub]

From:

if (!mergeTo.ContainsKey(pair.Key))
{
      mergeTo[pair.Key] = pair.Value;
}

To:

mergeTo.TryAdd(pair.Key, pair.Value);

The implementations are different, which is faster?

[yufeih]

From:

if (!mergeTo.ContainsKey(pair.Key))
{
      mergeTo[pair.Key] = pair.Value;
}

To:

mergeTo.TryAdd(pair.Key, pair.Value);

The implementations are different, which is faster?

TryAdd is faster, it computes hash code once.