How do you avoid or handle nulls in the Spectral bands we get from Landsat images through Earth Engine API

[rheashetty87]

I wrote a program to fetch Landsat 8 surface reflectance bands from Earth Engine Python API. Then stored this bands in Xarray, and finally a pandas dataframe. I get a lot of NANs, is it error in the code or I need to use some parameters in the code to avoid nulls in my final dataset. Note : I have filtered by region of interest and date(only one month)