Update Predicates.cs (#300)

Without the given treatment, entities without a namespace (global), generate an error at startup when creating the ServiceProvider

Author: gilbertogwa

src/AspectCore.Core/Configuration/Predicates.cs

@@ -10,8 +10,10 @@ public static AspectPredicate ForNameSpace(string nameSpace)
             {
                 throw new ArgumentNullException(nameof(nameSpace));
             }
-
-            return method => method.DeclaringType.Namespace.Matches(nameSpace);
+            
+            return method => nameSpace == method.DeclaringType.Namespace ||
+                             (method.DeclaringType.Namespace != null && 
+                              method.DeclaringType.Namespace.Matches(nameSpace));
         }
 
         public static AspectPredicate ForService(string service)
@@ -84,4 +86,4 @@ public static AspectPredicate Implement(Type baseOrInterfaceType)
             return methodInfo => baseOrInterfaceType.IsAssignableFrom(methodInfo.DeclaringType);
         }
     }
-}
+}