human
Solve the following python programming problem given the following code:
@ ApplyToDataframe 
def mutate(**kwargs) : 
    'Adds a column to the DataFrame.

  This can use existing columns of the DataFrame as input.

  In : (diamonds >> 
          mutate(carat_bin=X.carat.round()) >> 
          group_by(X.cut, X.carat_bin) >> 
          summarize(avg_price=X.price.mean()))
  Out:
         avg_price  carat_bin        cut
  0     863.908535          0      Ideal
  1    4213.864948          1      Ideal
  2   12838.984078          2      Ideal
  ...
  27  13466.823529          3       Fair
  28  15842.666667          4       Fair
  29  18018.000000          5       Fair
  ' 
    def addColumns(df) : 
        for (key, val) in six.iteritems (kwargs) : 
            if (type (val) == Later) : 
                df [key] = val.applyFcns (df) 
else : 
                df [key] = val 
return df 
return kwargs 

    
    

    Fix the buggy line: return kwargs
assistant
#Here is Python code to fix the buggy line: return kwargs
.

return def addColumns(