NPE on Blogposts and (Inline) Comments displayed to user

[tosts]

Upgraded Confluence Server 7.3.5 -> 7.13.2
& digital-signatures 7.0.2 -> 7.0.3

When testing to sign a macro on a blog post, a 500 xml error for a NullPointerException is displayed.
The macro did receive the signing, though.
Regular confluence pages do not exhibit this problem.

The instance contains additional plugins related to blog posts:

• Linchpin Enterprise News
• (maybe) News Teaser for Confluence
  The blog post in question was regular and fully published, though.

URL's like /rest/signature/1.0/sign?key=signature.a8ac9c5ed978910021be7258321a26cc5d929985cb44553b4ee202fd92ff2c50

This XML file does not appear to have any style information associated with it. The document tree is shown below.
<status>
<status-code>500</status-code>
<stack-trace>java.lang.NullPointerException
at com.baloise.confluence.digitalsignature.rest.DigitalSigatureService.sign(DigitalSigatureService.java:109)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at com.atlassian.plugins.rest.common.interceptor.impl.DispatchProviderHelper$ResponseOutInvoker.lambda$_dispatch$0(DispatchProviderHelper.java:181)
at com.atlassian.plugins.rest.common.interceptor.impl.DispatchProviderHelper.lambda$invokeMethodWithInterceptors$0(DispatchProviderHelper.java:81)
at com.atlassian.plugins.rest.common.interceptor.impl.DefaultMethodInvocation.invoke(DefaultMethodInvocation.java:53)
at com.atlassian.plugins.rest.common.expand.interceptor.ExpandInterceptor.intercept(ExpandInterceptor.java:42)
at com.atlassian.plugins.rest.common.interceptor.impl.DefaultMethodInvocation.invoke(DefaultMethodInvocation.java:53)
at com.atlassian.plugins.rest.common.interceptor.impl.DispatchProviderHelper.invokeMethodWithInterceptors(DispatchProviderHelper.java:106)
at com.atlassian.plugins.rest.common.interceptor.impl.DispatchProviderHelper$ResponseOutInvoker._dispatch(DispatchProviderHelper.java:180)
at com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:75) at com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:302)
at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147)
at com.sun.jersey.server.impl.uri.rules.ResourceClassRule.accept(ResourceClassRule.java:108)
...

Nothing shows up in the server log files, apart from the stacktrace also shown to the user.

Following the last comment on #65 a clearing of the plugin cache did not help with the error being shown.
(Also note that the exception is different from #65 & #68.)

[tosts]

The error also occures if the macro is used in a page comment. (both on regular pages & blog posts)
And even when used in inline comments. (Use copy-paste from e.g. a comment)

Though the last one is so exotic, that it's probably not a valid use case.
Still, not throwing stack traces at users is always nice. :)

[tosts]

Testing with the live system, at least the error shown when used in a page comment also exists in Confluence Server 7.3.5 with 7.0.2.
... so ... at least no regression! 😢