Working with missing data, pandas development team, 2024 - Official guide to handling missing values (NaN, None) in Pandas, including detection methods like isnull() and isna().
Python for Data Analysis, Wes McKinney, 2022 (O'Reilly Media) - A foundational book for data manipulation with Pandas, covering identification and handling of missing data comprehensively.
seaborn.heatmap, Michael Waskom and the Seaborn development team, 2024 - Official documentation for creating heatmaps, useful for visualizing patterns of missing data across a DataFrame using df.isnull().