Where did variable = null as “object destroying” come from?

Question

Working on a number of legacy systems written in various versions of .NET, across many different companies, I keep finding examples of the following pattern:

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Answer 1

It comes from C/C++ where explicitly made setting your pointers to null was the norm (to eliminate dangling pointers)

After calling free():

#include 
{
    char *dp = malloc ( A_CONST );

    // Now that we're freeing dp, it is a dangling pointer because it's pointing
    // to freed memory
    free ( dp );

    // Set dp to NULL so it is no longer dangling
    dp = NULL;
}

Classic VB developers also did the same thing when writing their COM components to prevent memory leaks.