تمرين: تنظيف البيانات

+---------+----+---+------+------+------------+
|id_number|name|age|gender|income|credit_score|
+---------+----+---+------+------+------------+
|   135245|John| 25|     M| 50000|        null|
|   223452|Jane| 30|     F| 60000|         700|
|   341412| Joe| 35|     M| 70000|         800|
|   341412| Joe| 35|     M| 70000|         800|
|   574355|Jill| 40|     F| 80000|         900|
|   253774|Jack| 45|     M| 90000|        1000|
|   856585|Jack| 75|     M|  null|         300|
+---------+----+---+------+------+------------+