diff --git a/core/src/main/java/org/kohsuke/stapler/bind/BoundObjectTable.java b/core/src/main/java/org/kohsuke/stapler/bind/BoundObjectTable.java
index <HASH>..<HASH> 100644
--- a/core/src/main/java/org/kohsuke/stapler/bind/BoundObjectTable.java
+++ b/core/src/main/java/org/kohsuke/stapler/bind/BoundObjectTable.java
@@ -120,7 +120,7 @@ public class BoundObjectTable implements StaplerFallback {
                 WithWellKnownURL w = (WithWellKnownURL) target;
                 String url = w.getWellKnownUrl();
                 if (!url.startsWith("/")) {
-                    throw new IllegalArgumentException("WithWellKnownURL.getWellKnownUrl must start with a slash: " + url);
+                    LOGGER.warning("WithWellKnownURL.getWellKnownUrl must start with a slash. But we got " + url + " from "+w);
                 }
                 return new WellKnownObjectHandle(url, w);
             }
Reducing this down to a warning.

I noticed that cloudbees wasted minute tracker causes this error, and it's a Widget, so if this is an exception, it'll break all the installations as soon as it upgrades.

Since this is meant to be caused by a programmer while in development, it's much better to issue a warning so that users will not be penalized.