Not provided doctrine types for nullable database type

[demenkov]

Such as

• Nullable(String)
• Nullable(Float64)
• Nullable(Int32)
• Array(Nullable(String))
• Nullable(UInt8)

etc.

[demenkov]

It isn't documented yet, but exists https://github.com/yandex/ClickHouse/issues/867

[mochalygin]

@demenkov How does it work? Where syntax examples can be found?

[demenkov]

@mochalygin

some info can be found here https://github.com/yandex/ClickHouse/blob/933313aea3d4fa1c217e4191b005055cf6caad0a/doc/example_datasets/nyc_taxi.md

sorry, I can't find example for arrays, only issues such as https://github.com/yandex/ClickHouse/issues/1028

[argayash]

@demenkov @mochalygin I think it's a good idea to use the notnull option in false mode to support Nullable ClickHouse types

added test