URI type does not allow NULL value to be set.

[silentninja]

Description

A column with the URI type does not allow null value to be set after creation even though the column nullable option is enabled

Expected behaviour

Allow setting a null value to a nullable URI type column without throwing up an error

To Reproduce

1. Create a new column with the type URI.
2. Try setting a null value to the column by creating a new row and not entering any data.
3. New row does not get created due to an error with URI type not accepting a null value