Description:
when using unoconv convert some docx, or using swriter open some docx, this error happen.

centos 7.7
# ./unoconv test.docx 
E: lt_string_value: assertion `string != ((void *)0)' failed
E: lt_string_value: assertion `string != ((void *)0)' failed
E: lt_string_value: assertion `string != ((void *)0)' failed
E: lt_string_value: assertion `string != ((void *)0)' failed

# /opt/libreoffice6.4/program/swriter aaa.docx 
Failed to open display
E: lt_string_value: assertion `string != ((void *)0)' failed
E: lt_string_value: assertion `string != ((void *)0)' failed
E: lt_string_value: assertion `string != ((void *)0)' failed
E: lt_string_value: assertion `string != ((void *)0)' failed

test libreoffice version, the same problem:
LibreOffice 5.3.6.1 30(Build:1)
LibreOffice 6.4.2.2


test in MACOX catalina, libreoffice 6.4.1.2:
soffice --writer /Users/monyer/Downloads/test.docx 
E: const char *lt_string_value(const lt_string_t *): assertion `string != ((void*)0)' failed
E: const char *lt_string_value(const lt_string_t *): assertion `string != ((void*)0)' failed
E: const char *lt_string_value(const lt_string_t *): assertion `string != ((void*)0)' failed
E: const char *lt_string_value(const lt_string_t *): assertion `string != ((void*)0)' failed

the same problem.

Steps to Reproduce:
1./opt/libreoffice6.4/program/swriter aaa.docx
2.
3.

Actual Results:
E: lt_string_value: assertion `string != ((void *)0)' failed
E: lt_string_value: assertion `string != ((void *)0)' failed
E: lt_string_value: assertion `string != ((void *)0)' failed
E: lt_string_value: assertion `string != ((void *)0)' failed



Expected Results:
no warning


Reproducible: Always


User Profile Reset: No



Additional Info:
版本: 6.4.1.2
Build ID: 4d224e95b98b138af42a64d84056446d09082932
CPU 线程: 8; 操作系统: Mac OS X 10.15.3; UI 渲染: 默认; VCL: osx; 
区域语言: zh-CN (zh_Hans.UTF-8); UI 语言: zh-CN
Calc: threaded