diff --git a/avaje-config/src/main/java/io/avaje/config/CoreEntry.java b/avaje-config/src/main/java/io/avaje/config/CoreEntry.java
index 81b7e82a..45dfc7bf 100644
--- a/avaje-config/src/main/java/io/avaje/config/CoreEntry.java
+++ b/avaje-config/src/main/java/io/avaje/config/CoreEntry.java
@@ -188,7 +188,7 @@ void put(String key, CoreEntry value) {
       entryMap.put(key, value);
     }
 
-    void put(String key, String value, String source) {
+    void put(String key, @Nullable String value, String source) {
       entryMap.put(key, CoreEntry.of(value, source));
     }
 
diff --git a/avaje-config/src/main/java/io/avaje/config/InitialLoadContext.java b/avaje-config/src/main/java/io/avaje/config/InitialLoadContext.java
index 5c0fbd90..6e26cda1 100644
--- a/avaje-config/src/main/java/io/avaje/config/InitialLoadContext.java
+++ b/avaje-config/src/main/java/io/avaje/config/InitialLoadContext.java
@@ -88,14 +88,14 @@ InputStream resource(String resourcePath, InitialLoader.Source source) {
     if (source == InitialLoader.Source.RESOURCE) {
       is = resourceStream(resourcePath);
       if (is != null) {
-        loadedResources.add("resource:" + resourcePath);
+        loadedResources.add(source.key(resourcePath));
       }
     } else {
       File file = new File(resourcePath);
       if (file.exists()) {
         try {
           is = new FileInputStream(file);
-          loadedResources.add("file:" + resourcePath);
+          loadedResources.add(source.key(resourcePath));
           loadedFiles.add(file);
         } catch (FileNotFoundException e) {
           throw new UncheckedIOException(e);
diff --git a/avaje-config/src/main/java/io/avaje/config/InitialLoader.java b/avaje-config/src/main/java/io/avaje/config/InitialLoader.java
index dbfa651d..daa8244a 100644
--- a/avaje-config/src/main/java/io/avaje/config/InitialLoader.java
+++ b/avaje-config/src/main/java/io/avaje/config/InitialLoader.java
@@ -35,7 +35,10 @@ static Configuration.ExpressionEval evalFor(Properties properties) {
 
   enum Source {
     RESOURCE,
-    FILE
+    FILE;
+    String key(String path) {
+      return name().toLowerCase() + ':' + path;
+    }
   }
 
   private final ConfigurationLog log;
@@ -298,7 +301,7 @@ private boolean loadCustom(String resourcePath, Source source) {
   boolean loadCustomExtension(String resourcePath, ConfigParser parser, Source source) {
     try (InputStream is = resource(resourcePath, source)) {
       if (is != null) {
-        var sourceName = (source == RESOURCE ? "resource:" : "file:") + resourcePath;
+        var sourceName = source.key(resourcePath);
         parser.load(is).forEach((k, v) -> loadContext.put(k, v, sourceName));
         return true;
       }
@@ -311,7 +314,7 @@ boolean loadCustomExtension(String resourcePath, ConfigParser parser, Source sou
   boolean loadProperties(String resourcePath, Source source) {
     try (InputStream is = resource(resourcePath, source)) {
       if (is != null) {
-        loadProperties(is, (source == RESOURCE ? "resource:" : "file") + resourcePath);
+        loadProperties(is, source.key(resourcePath));
         return true;
       }
     } catch (IOException e) {