Support null values in the middle of the payload

src/IEC6205675.cpp

@@ -391,7 +391,8 @@ CosemData* IEC6205675::getCosemDataAt(uint8_t index, const char* ptr) {
                 pos += 5;
                 break;
             case CosemTypeNull:
-                return NULL;
+                pos += 1;
+                break;
             default:
                 pos += 2;
         }