code: def null_column_constraint(self, tree):
      return ColumnConstraintEnum.NOTNULL
  
imports: from lark import Tree
  from evadb.catalog.catalog_type import ColumnType, NdArrayType, VectorStoreType
  from evadb.expression.tuple_value_expression import TupleValueExpression
  from evadb.parser.create_index_statement import CreateIndexStatement
  from evadb.parser.create_statement import ColConstraintInfo, ColumnDefinition, CreateDatabaseStatement, CreateJobStatement, CreateTableStatement
  from evadb.parser.table_ref import TableRef
  from evadb.parser.types import ColumnConstraintEnum
label_desc: Use image node_id 6 for calling the CreateTable obj's underlying member method code with example usage: obj.null_column_constraint(tree) and returns: ColumnConstraintEnum