In some situations, data may be declared as nullable. Nullable data can take on a “non-value”, for example, NULL in C, None in Python, or null in Java. Conversely, non-nullable data cannot be NULL. Only data of type opaque, string, secret, array, or structure may be declared nullable. Additionally, only structure fields and certain API types can be nullable. Specifically, array data cannot be nullable because the array type is actually more like a list than an array.