Chirag is right, you need to get this information by querying the system views. The result you are getting is the result of a query. Whether a returned column is nullable does not really make sense in this context.
e.g. if your query is (select 1 as a) is "a" nullable? The datatype can be sent back to you, and this is the reason you do not see a "IsNullable" property. I.e. the query may get the data from a number of tables, may aggregate result, may contain constants, etc. It is there to consume, but nullability is a constraint, and is used when you set values.
Andras Belokosztolszki, MCPD, PhD