diff --git a/racket-webview.rkt b/racket-webview.rkt
index 47c6207..96bae6a 100644
--- a/racket-webview.rkt
+++ b/racket-webview.rkt
@@ -718,10 +718,11 @@
                       (wv-win-window-nr wv) sel evt (if no-prevent-default 'true 'false)))
            (r (webview-call-js wv j))
            )
-      ;(dbg-webview "called js: ~a" j)
-      (map (λ (el)
-             (list (string->symbol (car el)) (cadr el) (caddr el)))
-           r))))
+      (if (eq? r #f)
+          #f
+          (map (λ (el)
+                 (list (string->symbol (car el)) (cadr el) (caddr el)))
+               r)))))
 
 (define/contract (webview-unbind! wv selector event)
   (-> wv-win? (or/c symbol? string?) (or/c symbol? list-of-symbol?) list?)
@@ -735,9 +736,11 @@
     (let ((r (webview-call-js wv
                               (format "return window.rkt_unbind_evt_ids(~a, '~a', ~a)"
                                       (wv-win-window-nr wv) sel evt))))
-      (map (λ (el)
-             (list (string->symbol (car el)) (cadr el) (caddr el)))
-           r))))
+      (if (eq? r #f)
+          #f
+          (map (λ (el)
+                 (list (string->symbol (car el)) (cadr el) (caddr el)))
+               r)))))
 
 (define/contract (webview-run-js wv js)
   (-> wv-win? string? symbol?)
@@ -857,7 +860,7 @@
 
 
 (define/contract (webview-add-class! wv id-or-selector class)
-  (-> wv-win? (or/c symbol? string?) (or/c symbol? string? list?) hash?)
+  (-> wv-win? (or/c symbol? string?) (or/c symbol? string? list?) (or/c hash? boolean?))
   (let ((sel (if (symbol? id-or-selector)
                  (format "#~a" id-or-selector)
                  id-or-selector))
@@ -877,7 +880,7 @@
   )
 
 (define/contract (webview-remove-class! wv id-or-selector class)
-  (-> wv-win? (or/c symbol? string?) (or/c symbol? string? list?) hash?)
+  (-> wv-win? (or/c symbol? string?) (or/c symbol? string? list?) (or/c hash? boolean?))
   (let ((sel (if (symbol? id-or-selector)
                  (format "#~a" id-or-selector)
                  id-or-selector))
@@ -899,7 +902,7 @@
   )
 
 (define/contract (webview-set-style! wv selector style-entries)
-  (-> wv-win? (or/c symbol? string?) (or/c kv? list-of-kv?) hash?)
+  (-> wv-win? (or/c symbol? string?) (or/c kv? list-of-kv?) (or/c hash? boolean?))
   (let ((sel (if (symbol? selector)
                  (format "#~a" selector)
                  selector))
@@ -945,18 +948,20 @@
                          "  return { id: id, style: r };"
                          "}") cl))
                      )))
-      (let ((h (hash-ref r 'with-ids)))
-        (let ((l (map (λ (e) (cons (string->symbol (hash-ref e 'id)) (hash-ref e 'style))) h)))
-          (if (symbol? selector)
-              (cdr (car l))
-              l)))
+      (if (eq? r #f)
+          #f
+          (let ((h (hash-ref r 'with-ids)))
+            (let ((l (map (λ (e) (cons (string->symbol (hash-ref e 'id)) (hash-ref e 'style))) h)))
+              (if (symbol? selector)
+                  (cdr (car l))
+                  l))))
       )
     )
   )
     
 
 (define/contract (webview-unset-style! wv selector style-entries)
-  (-> wv-win? (or/c symbol? string?) (or/c symbol? list-of-symbol?) hash?)
+  (-> wv-win? (or/c symbol? string?) (or/c symbol? list-of-symbol?) (or/c hash? boolean?))
   (let ((sel (if (symbol? selector)
                  (format "#~a" selector)
                  selector))
@@ -982,7 +987,7 @@
 
 (define/contract (webview-set-attr! wv selector attr-entries)
   (-> wv-win? (or/c symbol? string?)
-      (or/c kv? list-of-kv?) hash?)
+      (or/c kv? list-of-kv?) (or/c hash? boolean?))
   (let* ((sel (if (symbol? selector)
                   (format "#~a" selector)
                   selector))