code: def json_string(value) -> Expression:
      """
      Serializes a value into JSON.
  
      This function returns a JSON string containing the serialized value. If the value is `NULL`,
      the function returns `NULL`.
  
      Examples:
      ::
  
          >>> json_string(null_of(DataTypes.INT())) # None
  
          >>> json_string(1)               # '1'
          >>> json_string(True)            # 'true'
          >>> json_string("Hello, World!") # '"Hello, World!"'
          >>> json_string([1, 2])          # '[1,2]'
      """
      return _unary_op("jsonString", value)
  
imports: from typing import Union
  from pyflink import add_version_doc
  from pyflink.java_gateway import get_gateway
  from pyflink.table.expression import Expression, _get_java_expression, TimePointUnit, JsonOnNull
  from pyflink.table.types import _to_java_data_type, DataType
  from pyflink.table.udf import UserDefinedFunctionWrapper
  from pyflink.util.java_utils import to_jarray, load_java_class
label_desc: Use image node_id 52 for calling a global function with example usage: json_string(value) and returns: _unary_op