Handle null/empty strings correctly - ignore them ideally

Very minor point but I wonder if there should be some sort of undefined output from API level for this sort of thing? two null strings being classifed as 100% similar - I mean they are, but it doesn't feel like it's the right response?https://harmonydata.ac.uk/app/#/model/OkY4K8AEetIBHboCPDWB