$ perl -Mre=debug -ce ' /a{,5}/'
Compiling REx "a{,5}"
Final program:
   1: EXACT <a{,5}> (4)
   4: END (0)
anchored "a{,5}" at 0 (checking anchored isall) minlen 5 
-e syntax OK
Freeing REx: "a{,5}"

$ perl -wE 'say "yes" if "a{,4}" =~ /a{,4}/'
yes

# in contrast:
$ perl -Mre=debug -ce ' /a{0,5}/'
Compiling REx "a{0,5}"
Final program:
   1: CURLY {0,5} (5)
   3:   EXACT <a> (0)
   5: END (0)
minlen 0 
-e syntax OK
Freeing REx: "a{0,5}"