Pydantic model errors in percentile calculator

**Actual Behaviour**

Exception occurred POST /api/percentiles/
wps-prod-493-xjndj (34): 3 validation errors for StationSummary
ffmc
Input should be a valid number [type=float_type, input_value=None, input_type=NoneType]
For further information visit https://errors.pydantic.dev/2.6/v/float_type
isi
Input should be a valid number [type=float_type, input_value=None, input_type=NoneType]
For further information visit https://errors.pydantic.dev/2.6/v/float_type
bui
Input should be a valid number [type=float_type, input_value=None, input_type=NoneType]
For further information visit https://errors.pydantic.dev/2.6/v/float_type

**Steps To Reproduce**

1. Go to percentile calculator
2. Request data for any station
3. See error above

**Screenshots**

If applicable, add screenshots to help explain your problem.

**Expected Behaviour**

No error occurs

Start at the /api/percentiles/ endpoint and inspect the StationSummary model, focusing on how ffmc, isi, and bui are populated for a station request. Reproduce the percentile calculator request and trace the returned values; done means the request completes without the reported Pydantic validation errors.

Written by the indexing model from the issue text.