诊断奇怪的错误

TemplateSyntaxError at /app/materials/list/

Caught FieldError while rendering: Cannot resolve keyword 'None' into
field. Choices are: creator, id, is_official, materialentry, name, slug,
taggedmaterial

这很奇怪啊。。为什么是模板渲染错误呢？
Merge branch 'material-tag-support'