human
Solve the following python programming problem given the following code:
@ staticmethod 
def many_to_many(ref_model, ref_name = None, backref_name = None, middle_table_name = None) : 
    'Class Decorator, add a many-to-many relationship between two SQLAlchemy models.
        Parameters:
            ref_table_name is the name of the destination table, it is NOT the one decorated by this method.
            ref_name is how this model reference the destination models.
            backref_name is how the destination model reference this model.
            middle_table_name is the middle table name of this many-to-many relationship.
        ' 
    if isinstance (ref_model, str) : 
        ref_model_name = ref_model 
else : 
        ref_model_name = ref_model.__name__ 
ref_table_name = StringUtil.camelcase_to_underscore (ref_model_name) 
    ref_name = (ref_name or '{0}s'.format (ref_table)) 
    def ref_table(cls) : 
        if backref_name : 
            cls._readable_names = backref_name 
if (not isinstance (ref_model, str)) : 
            ref_model._readable_names = ref_name 
            cls._many_to_models.append (ref_model) 
            ref_model._many_to_models.append (cls) 
table_name = cls._readable_name 
        my_middle_table_name = (middle_table_name or '{0}_{1}'.format (table_name, ref_table_name)) 
        if (table_name == ref_table_name) : 
            left_column_name = 'left_id' 
            right_column_name = 'right_id' 
else : 
            left_column_name = '{0}_id'.format (table_name) 
            right_column_name = '{0}_id'.format (ref_table_name) 
middle_table = Table (my_middle_table_name, Database.Base.metadata, Column (left_column_name, Integer, ForeignKey ('{0}.id'.format (table_name), ondelete = 'CASCADE'), primary_key = True), Column (right_column_name, Integer, ForeignKey ('{0}.id'.format (ref_table_name), ondelete = 'CASCADE'), primary_key = True)) 
        my_backref_name = (backref_name or '{0}s'.format (table_name)) 
        parameters = dict (secondary = middle_table, lazy = 'dynamic', backref = backref (my_backref_name, lazy = 'dynamic')) 
     ...

    
    

    Fix the buggy line: ref_name = (ref_name or '{0}s'.format (ref_table))
assistant
#Here is Python program to fix the buggy line: ref_name = (ref_name or '{0}s'.

ref_name = (ref_name or '{0}s'.format (ref_table_name))