Add Class info to failure exception (#3746)

Author: ccrvincent

Diff for: assertj-core/src/main/java/org/assertj/core/api/ClassLoadingStrategyFactory.java

@@ -65,7 +65,7 @@ static ClassLoadingStrategyPair classLoadingStrategy(Class<?> assertClass) {
         throw new IllegalStateException("Could not access package of " + assertClass, e);
       }
     } else {
-      throw new IllegalStateException("No code generation strategy available");
+      throw new IllegalStateException("No code generation strategy available for " + assertClass);
     }
   }