The following error message is generated by AddressSanitizer:

=================================================================
==25695==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x7f0495576783 bp 0x7ffc5b00bb10 sp 0x7ffc5b00ba60 T0)
==25695==The signal is caused by a READ memory access.
==25695==Hint: address points to the zero page.
#0 0x7f0495576782 in modp_b64_decode src/modp_b64.c:177
#1 0x55c166594d91 in testEmpty test/modp_b64_test.c:57
#2 0x55c166597849 in all_tests test/modp_b64_test.c:259
#3 0x55c166597a04 in main test/modp_b64_test.c:266
#4 0x7f049539c0b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
#5 0x55c16659441d in _start (modp_b64_test.unittest+0x141d)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV src/modp_b64.c:177 in modp_b64_decode
==25695==ABORTING