Nulls from HashMap.get(Object)

Question

I understand that I get the nulls because the Object is not in the map. But is there some elegant way to have it default to the empty String?
Right now, after I grab all my data into variable with HashMap.get(Object), I go and check each once for null, and assign it the empty String instead. This is a lot of lines of code for something that is so basic.
I know i could initialize them all to the empty string, and then for each variable, check the HashMap with containsKey(Object) before assigning with HashMap.get(Object). Now, would I be correct in assuming the compiler would optimize this for me and not actually check the HashMap twice for the same Object? And... even if that is the case, its still just as many lines of code.
Is there perhaps some more elegant way?
String exchange = parameterMap.get("exchange");
String messageType = parameterMap.get("messagetype");
String traderTimeStamp = parameterMap.get("traderTimeStamp");
String exchangeTimeStamp = parameterMap.get("exchangeTimeStamp");
String sequence = parameterMap.get("sequence");
String product = parameterMap.get("product");
String quantity = parameterMap.get("quantity");
String price = parameterMap.get("price");
if (exchange == null)
exchange = "";
if (messageType == null)
messageType = "";
if (traderTimeStamp == null)
traderTimeStamp = "";
if (exchangeTimeStamp == null)
exchangeTimeStamp = "";
if (sequence == null)
sequence = "";
if (product == null)
product = "";
if (quantity == null)
quantity = "";
if (price == null)
price = "";

Answer 1

You could first put "" for all potential keys.
Or you could create a helper method
public String nonNull(String s) {
  return (s != null) ? s : "";
String exchange = nonNull(parameterMap.get("exchange"));