Closes issue #12546: Allow \x00 as a fill character for builtin type __format__ methods.

diff --cc Lib/test/test_unicode.py
Simple merge

diff --cc Misc/NEWS
index 4b548590ffffffca994fd2e138aba0c1590902c5,240c6cc0ec796913604c7974bc8f6fee2d4804cb..01ad416f77386a945e21329af236dc2115eed313
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -32,8 -27,9 +32,11 @@@ Core and Builtin
  - Issue #20637: Key-sharing now also works for instance dictionaries of
    subclasses.  Patch by Peter Ingebretson.
  
 +- Issue #19995: %c, %o, %x, and %X now raise TypeError on non-integer input.
 +
+ - Issue #12546: Allow \x00 to be used as a fill character when using str, int,
+   float, and complex __format__ methods.
+ 
  Library
  -------