public void add(long key, double value) {

		try {
			if (this.contains(key)) {
				double oldValue = this.get(key);
				double newValue = oldValue + value;
				this.put(key, newValue);
			}
			else {
				this.put(key, value);
			}
		}
		catch (NoValueException e) {
			//can't happen do nothing
		}
	}
Adds the value to the stored value rather than replacing it.
Ghidra/Framework/Generic/src/main/java/ghidra/util/graph/AddableLongDoubleHashtable.java