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Description
There is a bug in pynamodb.connection.Connection.update_table where updating a global secondary index fails with:
Invalid type for parameter GlobalSecondaryIndexUpdates[0].Update.ProvisionedThroughput.WriteCapacityUnits, value: None, type: <type 'NoneType'>, valid types: <type 'int'>, <type 'long'>
Invalid type for parameter GlobalSecondaryIndexUpdates[0].Update.ProvisionedThroughput.ReadCapacityUnits, value: None, type: <type 'NoneType'>, valid types: <type 'int'>, <type 'long'>
When comparing with the create_table() function, it's clear that the READ_CAPACITY_UNITS and WRITE_CAPACITY_UNITS keys are "converted" to camel case when they are already in camel case.
Here: https://github.com/jlafon/PynamoDB/blob/devel/pynamodb/connection/base.py#L435