code: def test_error_when_null_values_in_variable(df_vartypes):
      df_na = df_vartypes.copy()
      df_na.loc[1, "Age"] = np.nan
  
      transformer = RelativeFeatures(
          variables=["Age", "Marks"],
          reference=["Age", "Marks"],
          func=["add", "mul"],
          missing_values="raise",
      )
  
      with pytest.raises(ValueError):
          transformer.fit(df_na)
  
      transformer.fit(df_vartypes)
      with pytest.raises(ValueError):
          transformer.transform(df_na)
  
imports: import numpy
  import pandas
  import pytest
  from sklearn.pipeline import Pipeline
  from feature_engine.creation import RelativeFeatures
label_desc: Use image node_id 13 for calling a global function with example usage: test_error_when_null_values_in_variable(df_vartypes) without return types