code: def _runtime_zero_iterations_errmsg(symbol_names, nulls, init_vars):
      """Creates an error message asking for the loop to iterate at least once."""
      var_names = []
      for sn, n, v in zip(symbol_names, nulls, init_vars):
          if not n:
              continue
          if isinstance(v, variables.UndefinedReturnValue):
              var_names.append("the function return value")
          else:
              var_names.append(sn)
      var_names = ", ".join(var_names)
      return "loop must iterate at least once to initialize {}".format(
          var_names
      )
  
imports: import functools
  import sys
  import traceback
  import numpy
  from tensorflow.python.autograph.operators import py_builtins
  from tensorflow.python.autograph.operators import variables
  from tensorflow.python.autograph.utils import ag_logging
  from tensorflow.python.autograph.utils import misc
  from tensorflow.python.autograph.utils import tensors
  from tensorflow.python.autograph.utils import type_registry
  from tensorflow.python.framework import dtypes
  from tensorflow.python.framework import errors_impl
  from tensorflow.python.framework import func_graph
  from tensorflow.python.framework import ops
  from tensorflow.python.framework import tensor_conversion
  from tensorflow.python.framework import tensor_shape
  from tensorflow.python.framework import tensor_util
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import cond
  from tensorflow.python.ops import control_flow_assert
  from tensorflow.python.ops import control_flow_util
  from tensorflow.python.ops import math_ops
  from tensorflow.python.ops import tensor_array_ops
  from tensorflow.python.ops import while_loop
  from tensorflow.python.types import distribute
  from tensorflow.python.util import nest
  from tensorflow.python.util import variable_utils
label_desc: Use image node_id 22 for calling a global function with example usage: _runtime_zero_iterations_errmsg(symbol_names, nulls, init_vars) and returns: str