add error handling on dx==None  when writing
add error handling on dx==None  when writing

SasView/sasview,SasView/sasview,SasView/sasview,lewisodriscoll/sasview,SasView/sasview,SasView/sasview,lewisodriscoll/sasview,lewisodriscoll/sasview,SasView/sasview,lewisodriscoll/sasview,lewisodriscoll/sasview