You can flag columns as nullable for metadata purposes. To flag a column as nullable, specify the #notNull element after the data type element, separated by a comma. Note that columns marked with #key (primary key) element are read-only by default.

In the following example, the postion_title column has been designated as nullable, and the employeeID column is nullable because it has been designated the primary key.

{
"my_table":{
           "#path":[
               "https://example.com/employees"
          ],
          "employeeID":"VarChar(32),#key",
          "position_title":"VarChar(46),#notNull",
          "start_year":"Integer"
           }
}