'numpy.ndarray' object has no attribute 'notnull'

`numpy.ndarray` does not have a `notnull` attribute. The `notnull()` function is part of the pandas library, not NumPy. If you want to check for non-null values in a NumPy array, you can use the `numpy.isnan()` function to check for NaN (Not a Number) values. For example:

import numpy as np

arr = np.array([1, 2, np.nan, 4, 5])

# Check for non-null values
not_null_mask = ~np.isnan(arr)

print(arr[not_null_mask])  # Prints: [1. 2. 4. 5.]

Note that this will only work for arrays with numerical values, as `isnan()` specifically checks for NaN values.