The null-* subprofiles are automatically created by the kernel if a program in complain mode executes another program, and there's no execute rule (ix, Px, Cx or Ux) for that yet.
There should be a line with operation="exec" some lines above the lines you pasted that show what exactly gets executed, but the comm= part can also give you a hint. In your examples, something in your DEFAULT_URI hat executes sh and sendmail, and both want to write something to /dev/null.
The null-* subprofiles are automatically created by the kernel if a program in complain mode executes another program, and there's no execute rule (ix, Px, Cx or Ux) for that yet.
There should be a line with operation="exec" some lines above the lines you pasted that show what exactly gets executed, but the comm= part can also give you a hint. In your examples, something in your DEFAULT_URI hat executes sh and sendmail, and both want to write something to /dev/null.