Crash when doing 'create-period'

[ac000]

$ ./itsa create-period 
[INFO] ***
[INFO] *** Using TEST API
[INFO] ***

AddressSanitizer:DEADLYSIGNAL
=================================================================
==42598==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x7f1995eb9715 bp 0x7ffd27b8dd90 sp 0x7ffd27b8d528 T0)
==42598==The signal is caused by a READ memory access.
==42598==Hint: address points to the zero page.
    #0 0x7f1995eb9715 in __strlen_avx2 (/lib64/libc.so.6+0x160715)
    #1 0x7f19960ea8a1 in strdup (/lib64/libasan.so.6+0x598a1)
    #2 0x557d224244ef in get_period /home/andrew/programming/itsa/src/itsa.c:1656
    #3 0x557d224244ef in create_period /home/andrew/programming/itsa/src/itsa.c:1674
    #4 0x557d224244ef in dispatcher /home/andrew/programming/itsa/src/itsa.c:2277
    #5 0x557d224244ef in main /home/andrew/programming/itsa/src/itsa.c:2346
    #6 0x7f1995d80b74 in __libc_start_main (/lib64/libc.so.6+0x27b74)
    #7 0x557d22425a7d in _start (/home/andrew/programming/itsa/src/itsa+0x5a7d)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (/lib64/libc.so.6+0x160715) in __strlen_avx2
==42598==ABORTING

gdb backtrace

(gdb) bt full
#0  __strlen_avx2 () at ../sysdeps/x86_64/multiarch/strlen-avx2.S:65
No locals.
#1  0x00007f953bfb8183 in __GI___strdup (s=0x0) at strdup.c:41
        len = <optimized out>
        new = <optimized out>
#2  0x0000560a7b6f54f0 in get_period (end=<synthetic pointer>, 
    start=<synthetic pointer>) at itsa.c:1656
        met = <optimized out>
        start_obj = 0x0
        end_obj = 0x0
        err = <optimized out>
        result = 0x560a7c755140
        obs = <optimized out>
        period = <optimized out>
        index = <optimized out>
        jbuf = 0x560a7c7744a0 "[\n    {\n        \"status_code\": 200,\n        \"status_str\": \"OK\",\n        \"url\": \"https://test-api.service.hmrc.gov.uk/obligations/details/MZ200944B/income-and-expenditure\",\n        \"method\": \"GET\",\n   "...
        result = <optimized out>
        obs = <optimized out>
        period = <optimized out>
        index = <optimized out>
        jbuf = <optimized out>
        err = <optimized out>
        out_free = <optimized out>
        met = <optimized out>
        start_obj = <optimized out>
        end_obj = <optimized out>
#3  create_period () at itsa.c:1674
        start = 0x0
        end = 0x0
        ret = 0
        err = <optimized out>
        start = <optimized out>
        end = <optimized out>
        ret = <optimized out>
        err = <optimized out>
#4  dispatcher (cfg=0x7fff4c65f840, argv=<optimized out>, argc=2)
    at itsa.c:2277
No locals.
#5  main (argc=2, argv=<optimized out>) at itsa.c:2346
        err = <optimized out>
        ret = 0
        flags = <optimized out>
        config_dir = "/home/andrew/.config/itsa", '\000' <repeats 2799 times>...
        log_level = 0x0
        fph_ops = {
          fph_device_id = 0x0,
          fph_user = 0x0,
          fph_tz = 0x0,
          fph_ipaddrs = 0x0,
          fph_ipaddrs_ts = 0x0,
          fph_macaddrs = 0x0,
          fph_srcip = 0x0,
          fph_srcip_ts = 0x0,
          fph_srcport = 0x0,
          fph_screens = 0x0,
          fph_window_sz = 0x0,
          fph_browser_plugins = 0x0,
          fph_browser_js_ua = 0x0,
          fph_browser_dnt = 0x0,
          fph_vendor_ip = 0x0,
          fph_vendor_fwd = 0x0,
          fph_ua = 0x0,
          fph_multi_factor = 0x0,
          fph_license_id = 0x0,
          fph_version = 0x0,
          fph_version_cli = 0x560a7b6f7150 <set_ver_cli>,
          fph_prod_name = 0x560a7b6f7140 <set_prod_name>,
          user_data = 0x0
        }
        cfg = {
          fph_ops = 0x7fff4c65f910,
          extra_hdrs = 0x560a7b6ff0a0 <extra_hdrs>,
          config_dir = 0x7fff4c65fad0 "/home/andrew/.config/itsa"
        }
(gdb)