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obj item;
if(!dict.TryGetValue(name, out item))
    return null;
return item;

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You can use ContainsKey:

if (dict.ContainsKey(key)) { ... }
or TryGetValue:

dict.TryGetValue(key, out value);
Update: according to a comment the actual class here is not an IDictionary but a PhysicalAddressDictionary, so the methods are Contains and TryGetValue but they work in the same way.

Example usage:

PhysicalAddressEntry entry;
PhysicalAddressKey key = c.PhysicalAddresses[PhysicalAddressKey.Home].Street;
if (c.PhysicalAddresses.TryGetValue(key, out entry))
{
    row["HomeStreet"] = entry;
}
Update 2: here is the working code (compiled by question asker)

PhysicalAddressEntry entry;
PhysicalAddressKey key = PhysicalAddressKey.Home;
if (c.PhysicalAddresses.TryGetValue(key, out entry))
{
    if (entry.Street != null)
    {
        row["HomeStreet"] = entry.Street.ToString();
    }
}