fix: handle afterLastProperty() correctly when no properties exist

src/main/java/org/codejive/properties/Properties.java

@@ -483,11 +483,10 @@ private void replaceValue(String key, String rawValue, String value) {
 
     // Add a new property to the end of the list of tokens
     private Cursor addNewKeyValue(String rawKey, String key, String rawValue, String value) {
-        Cursor pos = afterLastProperty();
-        if (pos.atStart()) {
-            // We're at the start, meaning there are no properties yet,
-            // but there might be comments, so we move forward again,
-            // skipping any header comments
+        Cursor pos;
+        if (values.isEmpty()) {
+            // There are no properties yet, but there might be comments,
+            // so insert after the header comments.
             pos = afterHeader();
             if (pos.atEnd()) {
                 // afterHeader() leaves at most one blank line after the last comment.
@@ -501,6 +500,8 @@ private Cursor addNewKeyValue(String rawKey, String key, String rawValue, String
                     pos.addEol(eolType);
                 }
             }
+        } else {
+            pos = afterLastProperty();
         }
         return addNewKeyValue(pos, rawKey, key, rawValue, value);
     }
@@ -1211,10 +1212,10 @@ public Cursor beforeFirstProperty() {
     }
 
     /**
-     * Returns a Cursor pointing to the position past the last property, or to {@code -1} if the
-     * `Properties` object is empty.
+     * Returns a Cursor pointing to the position past the last property. If no properties exist,
+     * behaves like {@link #beforeFirstProperty()}.
      *
-     * @return a Cursor pointing to the right position or {@code -1} if not found
+     * @return a Cursor pointing past the last property, or before the first property if none exist
      */
     public Cursor afterLastProperty() {
         // Track back from end until we encounter the last VALUE token
@@ -1224,9 +1225,10 @@ public Cursor afterLastProperty() {
         }
         // Make sure we're either at the start or we've found a property
         validate(pos.atStart() || pos.isType(PropertiesParser.Type.VALUE), pos);
-        if (!pos.atStart()) {
-            pos.next().nextIf(Token::isEol);
+        if (pos.atStart()) {
+            return beforeFirstProperty();
         }
+        pos.next().nextIf(Token::isEol);
         return pos;
     }
 

src/test/java/org/codejive/properties/TestProperties.java

@@ -1242,11 +1242,32 @@ void testAfterLastProperty() throws IOException {
         Properties keyOnly = Properties.loadProperties(new StringReader("alpha\n"));
         assertThat(keyOnly.afterLastProperty().atEnd()).isTrue();
 
-        Properties commentsOnly = Properties.loadProperties(new StringReader("# header\n\n"));
-        assertThat(commentsOnly.afterLastProperty().atStart()).isTrue();
         assertThat(new Properties().afterLastProperty().atStart()).isTrue();
     }
 
+    @Test
+    void testAfterLastPropertyWithoutProperties() throws IOException {
+        for (String input :
+                Arrays.asList("", "\n\n", "  ", "# header", "# header\n\n", "  # header\r\n\r\n")) {
+            Properties p = Properties.loadProperties(new StringReader(input));
+            assertThat(p.afterLastProperty().position())
+                    .as("Cursor position for %s", input)
+                    .isEqualTo(p.beforeFirstProperty().position());
+            assertThat(p.afterLastProperty().atEnd()).isTrue();
+        }
+    }
+
+    @Test
+    void testPutAfterLastPropertyWithoutProperties() throws IOException {
+        for (String eol : Arrays.asList("\n", "\r\n")) {
+            String given = "# header" + eol + eol;
+            Properties p = Properties.loadProperties(new StringReader(given));
+            p.put(p.afterLastProperty(), "put", "val");
+            expectStoreText(p, given + "put=val" + eol);
+            assertThat(p.getComment("put")).isEmpty();
+        }
+    }
+
     @Test
     void testCursor() throws IOException, URISyntaxException {
         Properties p = Properties.loadProperties(getResource("/test.properties"));