bson/src/main/org/bson/BsonDocument.java
public BsonNumber getNumber(final Object key, final BsonNumber defaultValue) {
        if (!containsKey(key)) {
            return defaultValue;
        }
        return get(key).asNumber();
    }
public BsonNumber getNumber(final Object key, final BsonNumber defaultValue) {
        if (!containsKey(key)) {
            return defaultValue;
        }
        return get(key).asNumber();
    }
If the document does not contain the given key, return the given default value.  Otherwise, gets the value of the key as a
BsonNumber.

@param key the key
@param defaultValue the default value
@return the value of the key as a BsonNumber
@throws org.bson.BsonInvalidOperationException if the document contains the key but the value is not of the expected type