code: def example_graph_1(feature_size=None):
      nlist = [1, 2, 3, 4, 5, 6]
      if feature_size is not None:
          features = np.ones((len(nlist), feature_size))
      else:
          features = []
  
      elist = [(1, 2), (2, 3), (1, 4), (3, 2), (5, 6), (1, 5)]
  
      return StellarGraph(
          pd.DataFrame(features, index=nlist),
          pd.DataFrame(elist, columns=["source", "target"]),
      )
  
imports: import pandas
  import pytest
  import numpy
  import tensorflow
  from stellargraph import StellarGraph
  from stellargraph.layer import GraphSAGE, GCN, GAT, HinSAGE, link_classification, link_regression
  from stellargraph.mapper import GraphSAGENodeGenerator, FullBatchNodeGenerator, HinSAGENodeGenerator, GraphSAGELinkGenerator, HinSAGELinkGenerator
  from stellargraph.ensemble import Ensemble, BaggingEnsemble
  from tensorflow.keras import layers, Model
  from tensorflow.keras.optimizers import Adam
  from tensorflow.keras.losses import categorical_crossentropy, binary_crossentropy
label_desc: Use image node_id 1 for calling a global function with example usage: example_graph_1(feature_size) and returns: StellarGraph