np.NaN -> np.nan (Error) - #1688

np.NaN -> np.nan (Error)
view(dtype) -> astype(dtype) (Warning)

🔬 Background

• Numpy obsoleted use of np.NaN in favor of np.nan
• Pandas deprecated use of view() in favor of astype()

🔮 Key changes

• Eliminated runtime errors and warnings by following dependency package maintainer's suggestions

📋 Review Checklist

• I have performed a self-review of my own code.
• I have commented my code, added docstrings and data types to function definitions.
• I have added pytests to check whether my feature / fix works.

Please make sure to follow our best practices in the Contributing guidelines.