errors are now sanitized in the app by default (must use options(shiny.sanitize.errors = FALSE) to override this behavior)

man/shiny-options.Rd

@@ -70,6 +70,12 @@ The default polling interval is 500 milliseconds. You can change this
     an arguably more intuitive arrangement for casual R users, as the name
     of a function appears next to the srcref where it is defined, rather than
     where it is currently being called from.}
+  \item{shiny.sanitize.errors}{If \code{TRUE} (the default), then normal
+    errors (i.e errors generated by \code{stop}) won't show up in the app; a
+    simple generic error message is printed instead (the error and strack trace
+    printed to the console remain unchanged). If you want this behavior in
+    general, but you DO want a particular error message to get displayed to the
+    user, please use \code{stopWithCondition} instead.}
 }
 }