When variables not allowed to be null are actually created with no data on Django

When variables not allowed to be null are actually created with no data on
Django

I was recently adding large amounts of data from a JSON file to my Django
"member" model. For this purpose I had to make most of my variables able
to take in null or blank in order to handle cases when the JSON file did
not have information on a specific variable etc etc.
event = models.CharField(max_length=200, blank=True, null=True)
tool = models.CharField(max_length=200, blank=True, null=True)
other = models.CharField(max_length=200)
protocol = models.CharField(max_length=200)
However, I accidentally forgot to change 2 variables for this purpose.
Surprisingly my objects were generated without a problem even when the
JSON data was not adding anything to this variables.
So here is my question(s):
How was the member object created when some variables that are not allowed
to be null, were actually null or at the very least had no data.
I thought this restriction was at the Database level but it seems here
like it is only for user submitted data since when I created the object
internally it actually allowed me to have several null/blank variables.
Is Django taking care of something behind the scenes for me?
I know this is a lot but I hope it makes sense.... thanks