class_docstr: Determines if a value is null.
  
  Examples:
      >>> is_null = IsNull()
      >>> is_null([1, None, 3]).tolist()
      [False, True, False]
code: def get_function(self):
      def isnull(array):
          return array.isnull()
  
      return isnull
  
imports: from woodwork.column_schema import ColumnSchema
  from woodwork.logical_types import Boolean
  from featuretools.primitives.base import TransformPrimitive
  from featuretools.utils.gen_utils import Library
label_desc: Use image node_id 1 for calling the IsNull obj's underlying member method code with example usage: obj.get_function() and returns: isnull, array