A very easy task for you!
You have to create a method, that corrects a given date string.
There was a problem in addition, so many of the date strings are broken.
Date-Format is european. That means "DD.MM.YYYY".
Some examples:
"30.02.2016" -> "01.03.2016"
"40.06.2015" -> "10.07.2015"
"11.13.2014" -> "11.01.2015"
"99.11.2010" -> "07.02.2011"
If the input-string is null or empty return exactly this value!
If the date-string-format is invalid, return null.
Hint: Correct first the month and then the day!
Have fun coding it and please don't forget to vote and rank this kata! :-) 
I have created other katas. Have a look if you like coding and challenges.
from datetime import datetime,timedelta
from re import fullmatch
def date_correct(date):
    if isinstance(date,str):
        if not date:return ""
        if fullmatch("\d{2}\.\d{2}\.\d{4}",date):
            day,month,year=map(int,date.split("."))
            extra_year,month=divmod(month-1,12)
            return (datetime(year+extra_year,month+1,1)+timedelta(day-1)).strftime("%d.%m.%Y")
from datetime import datetime,timedelta
from re import fullmatch
def date_correct(date):
    if isinstance(date,str):
        if not date:return ""
        if fullmatch("\d{2}\.\d{2}\.\d{4}",date):
            day,month,year=map(int,date.split("."))
            extra_year,month=divmod(month-1,12)
            return (datetime(year+extra_year,month+1,1)+timedelta(day-1)).strftime("%d.%m.%Y")