Address book folder creation failed

Greetings.

I have set up a new Kubuntu 18.04 installation on an extra test machine to try out 
everything before I move my work over to it. 

First off - Kontact and Kmail continuously crash especially when I add or tinker with the 
addressbook. So I did some research and found a suggestion to downgrade the linux 
kernel to a previous LTS version. Computers is not my core competency, but after some 
more work I managed to self-compile and install kernel version 4.4.132 and 4.9.102. That 
seems to have sorted out the instability with Kontact, Addressbook and Kmail. So I am 
using kernel version 4.9.102 right now and will try version 4.14 over the weekend when I 
have time to tinker.

Next off I have been trying to set up Kontact to work for me. This is a dealbreaker for me 
as I need to have a stable usable PIM on my computer. I have over 2000 active contacts 
and they are organised in several sub-folders in the addressbook.

Now when I import my addressbook it does not replicate the sub-folders on import and 
when I try to manually recreate the sub-folders I get the following message:

"Address book folder creation failed - Kontact
X Could not create addressbook folder: Unable to append mimetype for collection Media 
resourceId: 4"

"Media" being the sub-folder I am trying to create.

I have been looking for solutions on the internet, but can't find any. Assistance at this 
juncture will be appreciated.

Second - in an attempt to solve the above problem I have begun looking at compiling and 
installing a newer version of KDE pim than what comes with Kubuntu but I am stuck at the 
instruction:

Let's setup a "kde:" prefix for git commands. Add the following text to your ~/.gitconfig: 
[url "git://anongit.kde.org/"]
   insteadOf = kde:
[url "ssh://[email protected]/"]
   pushInsteadOf = kde:
I can't even find the file ~/.gitconfig to open. How do I add that text to the file?
Again there is nothing helpful I can find on the internet.

-- 
Regards,
Lex Middelberg