How does a MySQL stored function evaluate whether it gets a NULL value when using a dynamic value from a table?

In this case, when the stored function gets a NULL value, it will return NULL as the result. As can be seen from the example below, the record of student ‘Mohit’ has a NULL value. Now, when we apply the stored function "avg_marks" to this data, it will return NULL as the result.

mysql> Select * from Student_marks;
+-------+------+---------+---------+---------+
| Name  | Math | English | Science | History |
+-------+------+---------+---------+---------+
| Raman |   95 |      89 |      85 |      81 |
| Rahul |   90 |      87 |      86 |      81 |
| Mohit |   90 |    NULL |      86 |      81 |
+-------+------+---------+---------+---------+
3 rows in set (0.00 sec)

mysql> SELECT Avg_marks('Mohit') AS 'MOHIT_marks';
+-------------+
| MOHIT_marks |
+-------------+
|        NULL |
+-------------+
1 row in set (0.00 sec)

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