The unsigned dtypes mapped to String

[Sayan-Paul]

https://github.com/googledatalab/pydatalab/blob/master/google/datalab/bigquery/_schema.py#L108

The unsigned dtypes is mapped to 'String' datatype for BigQuery which is causing an error when inserting data in table from the same dataframe.

dtype('uint8') has dtype.kind as 'u' which gets marked as STRING and when inserting data we get following error:

Field <field_name> in data has type FLOAT but in table has type STRING.

Any specific reason why this mapping was created ?