Prevent an NPE if the doc reference is not populated
Prevent an NPE if the doc reference is not populated

romeara/spdx-tools,yevster/tools,goneall/SPDX-Tools,rtgdk/tools,goneall/SPDX-Tools,sschuberth/spdx-tools,yevster/tools,yevster/tools,rtgdk/tools,romeara/spdx-tools,romeara/spdx-tools,goneall/SPDX-Tools,yevster/tools,yevster/tools,rtgdk/tools,sschuberth/spdx-tools,sschuberth/spdx-tools,sschuberth/spdx-tools,sschuberth/spdx-tools