===== ISTEM =====
Using the `median` function from Python's standard `statistics` module, write `robust_center(values)` that returns the median of a list of numbers, or None for an empty list.

===== HAM YANIT =====
Here is a simple Python function using the `median` function from Python's standard `statistics` module.

```python
import statistics

def robust_center(values):
    if len(values) == 0:
        return None
    else:
        return statistics.median(values)
```

You can use this function to calculate the median of a list of numbers. For an empty list, it will return `None`.

```python
print(robust_center([1, 2, 3, 4, 5]))  # Output: 3
print(robust_center([]))  # Output: None
```