Contrary to popular belief, the null bitmap is not always present in data records. Here's an example of a data record that doesn't contain a null bitmap due to using sparse columns.

Sparse columns are stored entirely different from normal fixed length and variable length columns. This post demonstrates & parses the sparse vector structure which stores the sparse columns.

How do we distinguish a normal variable length column value from one containing a complex value like a row-overflow pointer, back pointer or a sparse vector?