public synchronized long getFirstPropertyIndex() throws NoSuchIndexException {
		if (hasProperty(0)) {
			return 0;
		}
		return getNextPropertyIndex(0);
	}
Get the first index where a property value exists.
@throws NoSuchIndexException when there is no property value for any index.
Ghidra/Framework/Generic/src/main/java/ghidra/util/map/ValueMap.java