def split_param_filter_index1(s):
    """
    Split a parameter name into the <string><number> components
    where <string> is the parameter name and <number> is the filter
    index (1-based). If there is no number at the end for a filter
    index, then return None for the second argument.

    Returns
    ----------
    param_name : str
        The name of the parameter.
    filt_index : int (or None)
        The 1-based filter index.
    
    """
    param_name = s.rstrip('123456789')
    if len(param_name) == len(s):
        filt_index = None
    else:
        filt_index = int(s[len(param_name):])

    return param_name, filt_index