code: def replaceFirstMissingValue(self, df, series):
      # print(self.mDefaultValue, type(self.mDefaultValue));
      # Be explicit here .... some integer index does not work.
      df.loc[df.index[0], series] = self.mDefaultValue
  
imports: import pandas
  import numpy
  from .None import Time
  from .None import Perf
  from .None import Plots
  from .None import Utils
  import sklearn
  import sklearn.preprocessing
  import sklearn.linear_model
  from sklearn.feature_selection import RFE
  from sklearn.linear_model import LinearRegression
label_desc: Use image node_id 3 for calling the cLag1Trend obj's underlying member method code with example usage: obj.replaceFirstMissingValue(df, series) without return types