fix null reference in breaking change attribute helper (#411)

Author: VeryEarly

src/Common/CustomAttributes/BreakingChangeAttributeHelper.cs

@@ -155,9 +155,11 @@ public static IEnumerable<GenericBreakingChangeWithVersionAttribute> GetAllBreak
                 attributeList.AddRange(f.GetCustomAttributes(typeof(GenericBreakingChangeWithVersionAttribute), false).Cast<GenericBreakingChangeWithVersionAttribute>());
             }
 
-            foreach (ParameterMetadata param in invocationInfo?.MyCommand?.Parameters?.Values)
-            {
-                attributeList.AddRange(param.Attributes.Where(a => a is GenericBreakingChangeWithVersionAttribute).Select(a => a as GenericBreakingChangeWithVersionAttribute));
+            if (invocationInfo?.MyCommand?.Parameters?.Values != null) {
+                foreach (ParameterMetadata param in invocationInfo.MyCommand.Parameters.Values)
+                {
+                    attributeList.AddRange(param.Attributes.Where(a => a is GenericBreakingChangeWithVersionAttribute).Select(a => a as GenericBreakingChangeWithVersionAttribute));
+                }
             }
 
             return invocationInfo == null ? attributeList : attributeList.Where(e => e.IsApplicableToInvocation(invocationInfo));