Suppose we have an API /getTransaction with following response

{
transactionId: “TCC1232434”,
bankName: “ABC”,
accountNumber: 12131314,
transactionComments: "comments"
}

We might have another API to create the transaction and generally, transactionComments is an optional field

So while creating a transaction if someone does not enter transaction comments, nothing is stored in the database for field transactionCommentswhich is equivalent to null

and thus calling /getTransaction will return

{   
transactionId: “TCC1232434”,
bankName: “ABC”,
accountNumber: 12131314,
transactionComments: null
}

Now consumer of API is expecting transactionComments to be a string, and so might have string methods applied on transactionCommentslike this transactionComments.replace(' ‘,' — ‘)

We could well apply null check at front-end, but the number of places where this null check has to be applied is incalculable, so this null check should be handled by API, not frontend code

Thus a valid API response in case transactionComments in database is null should be

{
transactionId: “TCC1232434”,
bankName: “ABC”,
accountNumber: 12131314,
transactionComments: null
}

So now when we have agreed over handling such checks at API level, we have to define a compatible null value as well

In our example ‘’ is a perfect null value for transactionComments and for other cases, we have to find a value which is not a valid value and define it as a null value like maybe 0 for account number assuming a valid account number can never be 0

The contract between front-end and backend is not broken due to value changes in the database

Please let me know your views.

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