RecurrenceRule.setByDayPart doesn't remove BYDAY part when given an empty list

Calling RecurrenceRule#setByDayPart with an empty list seems to include that empty list in the parts map — I believe it's due to a missing else or return in the method:

lib-recur/src/main/java/org/dmfs/rfc5545/recur/RecurrenceRule.java

Lines 1957 to 1965 in d59e866

    
           public void setByDayPart(List<WeekdayNum> value) 
        
           { 
        
               if (value == null || value.size() == 0) 
        
               { 
        
                   mParts.remove(Part.BYDAY); 
        
               } 
        
               mParts.put(Part.BYDAY, value); 
        
           }

This makes the resulting rule have an empty BYDAY-value, e.g. "FREQ=MONTHLY;BYMONTHDAY=31;BYDAY=", eventually leading to an "too many empty recurrence sets" exception when expanding the rule.

Admittedly, the setters never were a real use case for me so far, that's probably why they are so poorly tested. Thanks for reporting and fixing this. I hope there are no other bad surprises there.

	public void setByDayPart(List<WeekdayNum> value)
	{
	if (value == null \|\| value.size() == 0)
	{
	mParts.remove(Part.BYDAY);
	}

	mParts.put(Part.BYDAY, value);
	}