package io.undertow.servlet.api;

/**
 * @author Stuart Douglas
 */
public enum ServletStackTraces {

    NONE("none"),
    LOCAL_ONLY("local-only"),
    ALL("all");

    private final String value;

    private ServletStackTraces(String value) {
        this.value = value;
    }

    @Override
    public String toString() {
        return value;
    }
}

package io.undertow.servlet.api;

/**
 * @author Stuart Douglas
 */
public enum ServletStackTraces {

    NONE,
    LOCAL_ONLY,
    ALL
}

--- 
+++ 
@@ -5,7 +5,18 @@
  */
 public enum ServletStackTraces {
 
-    NONE,
-    LOCAL_ONLY,
-    ALL
+    NONE("none"),
+    LOCAL_ONLY("local-only"),
+    ALL("all");
+
+    private final String value;
+
+    private ServletStackTraces(String value) {
+        this.value = value;
+    }
+
+    @Override
+    public String toString() {
+        return value;
+    }
 }
Add string representation to enum
