In src/define/animation.js, properties.zoom may have a value like…

… `{ level: 1 }` if an invalid zoom level is specified. The application of a zoom animation to the current zoom level is invalid. For example, animating from zoom:1 to zoom:1 doesn't make sense.

When there is a case of an invalid zoom animation, the entire `zoom` animation value is discarded.  This voids the animation.

In the easing application routine, there is now an extra check for equal start and end values.  While this does not affect the code path for the zoom:1 to zoom:1 example, it adds an extra layer of safety.

Ref : Specifying a no-effect zoom animation causes an error #2614

src/core/animation/ease.js

@@ -5,6 +5,10 @@ function getEasedValue( type, start, end, percent, easingFn ){
     return end;
   }
 
+  if( start === end ){
+    return end;
+  }
+
   let val = easingFn( start, end, percent );
 
   if( type == null ){

src/define/animation.js

@@ -156,6 +156,8 @@ let define = {
           if( vp.zoomed ){ properties.zoom = vp.zoom; }
 
           if( vp.panned ){ properties.pan = vp.pan; }
+        } else {
+          properties.zoom = null; // an inavalid zoom (e.g. no delta) gets automatically destroyed
         }
       }