Fixed: deviation from cocoa when calling setTitle:'' (#2607)

AppKit/CPPopUpButton.j

@@ -491,9 +491,17 @@ CPPopUpButtonStatePullsDown = CPThemeState("pulls-down");
 
         if (index < 0)
         {
-            [self addItemWithTitle:aTitle];
 
-            index = [self numberOfItems] - 1;
+            // this ist to match cocoa where setting an empty string does not add it but simply clears the title
+            // and sets objectValue to -1
+            if (aTitle === '')
+                [self selectItemAtIndex:-1];
+            else
+            {
+                [self addItemWithTitle:aTitle];
+
+                index = [self numberOfItems] - 1;
+            }
         }
 
         [self selectItemAtIndex:index];

Tests/Manual/CPPopUpButtonTest/AppController.j

@@ -75,9 +75,24 @@
     // https://github.com/280north/cappuccino/pull/1018
     [popUpButton2 selectItemWithTag:2];
 
+    // manual test for https://github.com/cappuccino/cappuccino/issues/2471
+    var button2 = [CPButton buttonWithTitle:@"Set title to: ''"];
+
+    [button2 setCenter:CGPointMake([contentView center].x, 0)];
+    [button2 setFrameOrigin:CGPointMake(CGRectGetMinX([button frame]), CGRectGetMaxY([button frame]) + 20)];
+    [button2 setTarget:self];
+    [button2 setAction:@selector(setTitleToEmptyString:)];
+    [contentView addSubview:button2];
+
+
     [theWindow orderFront:self];
 }
 
+- (@action)setTitleToEmptyString:(id)sender
+{
+    [popUpButton setTitle:''];
+}
+
 - (@action)removeItems:(id)sender
 {
     [popUpButton2 removeAllItems];