User property can not be found causing a Nullpointer when trying to render a link

The error occurs on a page showing various team members of project, including photos of them. The page wasn't modified in the last few days before the error occurred.

2005-09-22 09:49:15 2005-09-22 09:49:15,583 FATAL [user.providers.jira.JiraJdbcProfileProvider] Could not find property set for username
2005-09-22 09:49:15,677 ERROR [atlassian.confluence.util.XWorkTransactionInterceptor] Invoking rollback for transaction on action '/pages/viewpage.action (ViewPageAction.execute())' due to throwable: java.lang.NullPointerException
java.lang.NullPointerException
at com.atlassian.renderer.v2.V2LinkRenderer.renderLink(V2LinkRenderer.java:54)
at com.atlassian.renderer.v2.components.link.LinkDecorator.render(LinkDecorator.java:41)
at com.atlassian.renderer.v2.components.TokenRendererComponent.appendSubstitution(TokenRendererComponent.java:58)
at com.atlassian.renderer.v2.components.AbstractRegexRendererComponent.regexRender(AbstractRegexRendererComponent.java:32)
at com.atlassian.renderer.v2.components.TokenRendererComponent.render(TokenRendererComponent.java:45)
at com.atlassian.renderer.v2.V2Renderer.render(V2Renderer.java:38)
at com.atlassian.renderer.v2.V2RendererFacade.convertWikiToXHtml(V2RendererFacade.java:53)
at sun.reflect.GeneratedMethodAccessor427.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:324)
at org.springframework.aop.framework.AopProxyUtils.invokeJoinpointUsingReflection(AopProxyUtils.java:61)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:149)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:116)
at com.atlassian.confluence.util.profiling.SpringProfilingInterceptor.invoke(SpringProfilingInterceptor.java:16)