Working with Missing Values with Airscript
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There are times when data may not have a value. For example, in an application that is designed to capture a user's address the variable holding the address will be empty until the user has filled in their address. Another example may be a user that doesn't have a middle name. Variables must always have a value, so is used to indicate that a certain piece of data is missing.
If you were to store the address a user enters in a variable called address and access that variable before the user has entered their address you would end up with the value NULL.
Taking this example a bit further, if you were to access a property from the address such as zip_code you would also end up with the value NULL.
If some of your data may be missing, it is a good idea to check if it is NULL before using it. For example, if you wanted to display the zip_code field to the user and there is no value it would be better to display a helpful message instead.
In the previous example, what would you display if the zip_code is the empty string ("")?. Well, we could of course also check for that.
However, it is much more convenient to use the function, which returns FALSE for both "", as well as NULL.
There is a companion function, so we could accomplish the same by changing the ordering.
This situation is not unique to strings, you may want to handle an empty list the same way you treat NULL. The following values are considered to be empty.
The null value: NULL
An empty list: []
An empty object: {}
An empty string: ""
The following values are considered falsey
Several types have a corresponding function that tells you whether or not a value is of that type.
The function, the WHERE clause of the , and the filtering Path Bindings all examine their values in terms of whether they are falsy or not. For example, the empty string ("") is falsy, so we did not need to use they function at all in our previous example.
You may not always know that a value will be of a certain type. For example, even though you asked the user to enter a phone number, they may have entered something else like "Hello Airkit!". Not only, can you not call a phone number like "Hello Airkit", a phone number must be in a very specific format in order to be called (or sent an SMS). The function will return TRUE when a string represents a phone number that can be called.