ParquetWriter Nullable Types

[MaxZ2033]

fixes #314
ParquetWriter assigns type nullable instead of type string to nullables.

[Imran-imtiaz48]

The code snippet, while functional, can be optimized for readability and maintainability. The repeated typeof(string) returns suggest a potential refactor to reduce redundancy. Grouping these similar conditions together or using a switch-case statement could enhance clarity. Additionally, incorporating comments to explain the rationale behind each condition would benefit future developers. Ensuring consistent formatting and adding a final else clause to handle unexpected types would also improve robustness. Overall, the code achieves its purpose but could be streamlined for better efficiency and comprehension.