code: def to_timestamp(
      timestamp_str: Union[str, Expression[str]],
      format: Union[str, Expression[str]] = None,
  ) -> Expression:
      """
      Converts the date time string with the given format (by default: 'yyyy-MM-dd HH:mm:ss')
      under the 'UTC+0' time zone to a timestamp.
  
      :param timestamp_str: The date time string
      :param format: The format of the string
      :return: The date value with TIMESTAMP type.
      """
      if format is None:
          return _unary_op("toTimestamp", timestamp_str)
      else:
          return _binary_op("toTimestamp", timestamp_str, format)
  
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 22 for calling a global function with example usage: to_timestamp(timestamp_str, format) and returns: _unary_op, _binary_op