Better handling of column lines with all values at NA

python/obitools3/format/header.pyx

@@ -56,9 +56,11 @@ cdef class HeaderFormat:
         for k in ktags:
             if k in tags:
                 value = data[k]
-                if value is None:
+                if value is None or (isinstance(value, Column_line) and value.is_NA()):
                     if self.printNAKeys:
                         value = self.NAString
+                    else:
+                        value = None
                 else:
                     if type(value) == Column_line:
                         value = value.bytes()