fix: guard against null in SimpleUri(String) and StringRepresentationTypeHandler

engine/src/main/java/org/terasology/engine/core/SimpleUri.java

@@ -58,11 +58,15 @@ public SimpleUri(Name moduleName, Name objectName) {
     }
 
     /**
-     * Creates a SimpleUri from a string in the format "module:object". If the string does not match this format, it will be marked invalid
+     * Creates a SimpleUri from a string in the format "module:object". If the string does not match this format
+     * (including {@code null}), it will be marked invalid.
      *
      * @param simpleUri
      */
     public SimpleUri(String simpleUri) {
+        if (simpleUri == null) {
+            return;
+        }
         String[] split = simpleUri.split(MODULE_SEPARATOR, 2);
         if (split.length > 1) {
             moduleName = new Name(split[0]);

subsystems/TypeHandlerLibrary/src/main/java/org/terasology/persistence/typeHandling/StringRepresentationTypeHandler.java

@@ -19,7 +19,15 @@ public PersistedData serializeNonNull(T value, PersistedDataSerializer serialize
     @Override
     public Optional<T> deserialize(PersistedData data) {
         if (data.isString()) {
-            return Optional.ofNullable(getFromString(data.getAsString()));
+            String value = data.getAsString();
+            if (value == null) {
+                // A PersistedData can report isString() true while still holding no actual
+                // content (e.g. a stale/renamed reference in older save data) - treat that the
+                // same as "absent" instead of forwarding null into getFromString(), which for
+                // handlers like ComponentClassTypeHandler ends up constructing a SimpleUri(null).
+                return Optional.empty();
+            }
+            return Optional.ofNullable(getFromString(value));
         }
         return Optional.empty();
     }