Add defaults for lineNameInfo text and fields

lib/www/client/source/src/components/decoder/fixed-string-decoder.vue

@@ -229,9 +229,9 @@ export default {
   ],
 
   props: {
-    text: String,
+    text: { type: String, default: "" },
     fixed: { type: Array, default: () => [] },
-    fields: Object,
+    fields: { type: Object, default: () => ({}) },
     multiline: Boolean,
     numberedLines: [ Boolean, Number ],
     maxHeight: String,