class_docstr: Base class for exploring graphs.
class_docstr_tok: ["Base","class","for","exploring","graphs","."]
code: def _check_nodes(self, nodes):
      if nodes is None:
          self._raise_error("A list of root node IDs was not provided.")
      if not is_real_iterable(nodes):
          self._raise_error(
              "Nodes parameter should be an iterable of node IDs."
          )
      if (
          len(nodes) == 0
      ):  # this is not an error but maybe a warning should be printed to inform the caller
          warnings.warn(
              "No root node IDs given. An empty list will be returned as a result.",
              RuntimeWarning,
              stacklevel=3,
          )
  
imports: import numpy
  import warnings
  from collections import defaultdict, deque
  from scipy import stats
  from scipy.special import softmax
  from ..core.schema import GraphSchema
  from ..core.graph import StellarGraph
  from ..core.utils import is_real_iterable
  from ..core.validation import require_integer_in_range, comma_sep
  from ..random import random_state
  from abc import ABC, abstractmethod
label_desc: Use image node_id 9 for calling the GraphWalk obj's underlying member method code with example usage: obj._check_nodes(nodes) without return types