**savedObjects:listingLimit** needs to have a clear button to reset to defaults

[bhavyarm]

Kibana version: 6.3.0 BC3

Elasticsearch version: 6.3.0 BC3

Server OS version: darwin_x86_64

Browser version: chrome latest

Browser OS version: OS X

Original install method (e.g. download page, yum, from source, etc.): from staging

Describe the bug: If user changes the value for savedObjects:listingLimit and then removes it, Kibana doesn't reset it to defaults. This breaks the listing table on saved objects/visualizations and dashboards.

Please note - the setting is also missing the clear button.

Steps to reproduce:

1. Go to advanced settings - search for savedObjects:listingLimit.
2. Notice that default is 1000 - change it to 25 - go to listing pages under visualize/dashboard/saved objects and verify the listing behaviour
3. Go back to advanced settings and delete 25 and save it. Notice the default 1000 again for the value
4. Try to access viz listing table - you cannot.
5. Go back to advanced settings and explicitly set the value to 1000. Listing table works fine.

Expected behavior: There should be a clear button to reset the setting and Kibana shouldn't break the listing page

Screenshots (if relevant):

Errors in browser console (if relevant):

vendors.bundle.js:133 GET http://localhost:5601/api/saved_objects/_find?type=visualization&per_page=&page=1&search_fields=title%5E3&search_fields=description 400 (Bad Request)
(anonymous) @ vendors.bundle.js:133
sendReq @ vendors.bundle.js:133
serverRequest @ vendors.bundle.js:133
processQueue @ vendors.bundle.js:133
(anonymous) @ vendors.bundle.js:133
$digest @ vendors.bundle.js:133
$apply @ vendors.bundle.js:133
wrapped @ vendors.bundle.js:14
(anonymous) @ kibana.bundle.js:7
complete @ vendors.bundle.js:3
delayed @ vendors.bundle.js:3
setTimeout (async)
debounced @ vendors.bundle.js:3
VisualizeListingTable._this.fetchItems @ kibana.bundle.js:7
value @ kibana.bundle.js:7
commitLifeCycles @ vendors.bundle.js:141
b @ vendors.bundle.js:141
m @ vendors.bundle.js:141
w @ vendors.bundle.js:141
z @ vendors.bundle.js:141
u @ vendors.bundle.js:141
updateContainer @ vendors.bundle.js:141
(anonymous) @ vendors.bundle.js:141
unbatchedUpdates @ vendors.bundle.js:141
Pg @ vendors.bundle.js:141
render @ vendors.bundle.js:149
(anonymous) @ vendors.bundle.js:14
$digest @ vendors.bundle.js:133
$apply @ vendors.bundle.js:133
(anonymous) @ vendors.bundle.js:133
dispatch @ vendors.bundle.js:128
elemData.handle @ vendors.bundle.js:128
vendors.bundle.js:133 Error: child "per_page" fails because ["per_page" must be a number]
    at commons.bundle.js:3
    at processQueue (vendors.bundle.js:133)
    at vendors.bundle.js:133
    at Scope.$digest (vendors.bundle.js:133)
    at Scope.$apply (vendors.bundle.js:133)
    at done (vendors.bundle.js:133)
    at completeRequest (vendors.bundle.js:133)
    at XMLHttpRequest.xhr.onload (vendors.bundle.js:133) "Possibly unhandled rejection: {"statusCode":400,"body":{"statusCode":400,"error":"Bad Request","message":"child \"per_page\" fails because [\"per_page\" must be a number]","validation":{"source":"query","keys":["per_page"]}}}"
(anonymous) @ vendors.bundle.js:133
(anonymous) @ vendors.bundle.js:133
processChecks @ vendors.bundle.js:133
$digest @ vendors.bundle.js:133
$apply @ vendors.bundle.js:133
done @ vendors.bundle.js:133
completeRequest @ vendors.bundle.js:133
xhr.onload @ vendors.bundle.js:133
load (async)
(anonymous) @ vendors.bundle.js:133
sendReq @ vendors.bundle.js:133
serverRequest @ vendors.bundle.js:133
processQueue @ vendors.bundle.js:133
(anonymous) @ vendors.bundle.js:133
$digest @ vendors.bundle.js:133
$apply @ vendors.bundle.js:133
wrapped @ vendors.bundle.js:14
(anonymous) @ kibana.bundle.js:7
complete @ vendors.bundle.js:3
delayed @ vendors.bundle.js:3
setTimeout (async)
debounced @ vendors.bundle.js:3
VisualizeListingTable._this.fetchItems @ kibana.bundle.js:7
value @ kibana.bundle.js:7
commitLifeCycles @ vendors.bundle.js:141
b @ vendors.bundle.js:141
m @ vendors.bundle.js:141
w @ vendors.bundle.js:141
z @ vendors.bundle.js:141
u @ vendors.bundle.js:141
updateContainer @ vendors.bundle.js:141
(anonymous) @ vendors.bundle.js:141
unbatchedUpdates @ vendors.bundle.js:141
Pg @ vendors.bundle.js:141
render @ vendors.bundle.js:149
(anonymous) @ vendors.bundle.js:14
$digest @ vendors.bundle.js:133
$apply @ vendors.bundle.js:133
(anonymous) @ vendors.bundle.js:133
dispatch @ vendors.bundle.js:128
elemData.handle @ vendors.bundle.js:128
**vendors.bundle.js:3 Config: config change: savedObjects:listingLimit: NaN -> 25
vendors.bundle.js:3 Config: config change: savedObjects:listingLimit: 25 ->** 

[bhavyarm]

cc @jen-huang thought you might be interested in looking at this :) Cheers!

[jen-huang]

This issue has likely existed for a while. Kibana 6.4 introduces a revamp of Advanced Settings #17465 where this behavior will not occur. Clearing out this setting in 6.4 will change it to 0 and there is a Reset to default link.

Since there is a workaround for <=6.3 by manually setting the value again, I'm closing this issue.