java.lang.java.lang.UnsupportedOperationException

[issues solution]

Hi ,
somone can tell  me why i get the folowing error  with udf apply  like udf

def replaceCempty(x):
    if x is None :
        return ""
    else :
        return x.encode('utf-8')
udf_replaceCempty = F.udf(replaceCempty,StringType())

dfTotaleNormalize53 = dfTotaleNormalize52.select([i if i not in
colprocessing  else  udf_replaceCempty(F.col(i)).alias(i) for i in
dfTotaleNormalize52.columns])


java.lang.java.lang.UnsupportedOperationException

 Cannot evaluate expression: PythonUDF#replaceCempty(input[77,string])

??
regards