code: def match_header(cls, header):
          
  
          pixvalue = header.get('PIXVALUE')
          naxis = header.get('NAXIS', 0)
  
          return (super(_ConstantValueImageBaseHDU, cls).match_header(header) and
                  (isinstance(pixvalue, float) or _is_int(pixvalue)) and
                  naxis == 0)
docs: A constant value HDU will only be recognized as such if the header
          contains a valid PIXVALUE and NAXIS == 0.