Working with missing data, pandas development team, 2023 - Explains fundamental Pandas functions for identifying and counting missing values, including isnull(), notnull(), isna(), notna(), and their application with sum().
Python for Data Analysis, Wes McKinney, 2022 (O'Reilly Media) - Offers a comprehensive treatment of missing data handling in Pandas, detailing detection, counting, and various imputation strategies.