The warning is quite self explanatory. The column 'Material_Qty' has a bigint type, meaning integers are the only valid data. However, it is being fed floats.
The error "Null pointer exception" is too generic. We would need job logs for that. However before doing that, this error is thrown when an application tries to use an object reference which has a null value. Consequently, I would suggest checking the data inputs to the recipe; Do the datasets exist? Do the columns have data? Is the data valid according to the schemas of the datasets? This is particularly important in the case of the join key s.