see http://sourceforge.net/p/ndoc3/discussion/763824/thread/5fc53f90/#c471
patch for ndoc3-code\src\Core\Core\Reflection\ExternalXmlSummaryCache.cs
Index: ExternalXmlSummaryCache.cs
===================================================================
--- ExternalXmlSummaryCache.cs (revision 371)
+++ ExternalXmlSummaryCache.cs (working copy)
@@ -305,7 +305,7 @@
: memberID.Substring(memberID.LastIndexOf('.') + 1);
//the member id in the declaring assembly
- string key = memberType + declaringType.FullName.Replace("+", ".") + "." + memberName;
+ string key = memberType + (declaringType.FullName ?? string.Empty).Replace("+", ".") + "." + memberName;
//check the summaries cache first
string summary = (string)summaries[key];