There are some reasons as follow:
you can use USB to connect to your computer,and then output the fault daily and analyse the reason,you can find:
1)whether you have the root privileges?
2) It is possible because you make the contacts be null.(Android system can't permit the contacts to be null and will give you the tips for the error.
3)come up the second situation,there are four reasons:
a>If you have the root privileges and make the contacts null(you can open the People to check it.If you can't open the apps,you can download the skype contact to check it)
b>the name of the contact is null,it's usually because of the outside problems instead of the operations of adding the contacts.
c>there are many reasons to lead the null problem,such as the name of google gmail to be null.
The solutions:
1)close Contacts,and clear the cache.
Setting——>APPs——>find contacts and contacts storage——>clear the cache of them(clear data)——>close both the apps(Disable)
2)delete teh null contacts
you can delete the whole unknown contacts and then choose delete.
3)restart the contacts
this step you can restart the contacts and the contacts storage which you have closed just know.
That's ok!
