I'm able to create a page with only spaces in title.

Location : https://extranet.atlassian.com/pages/viewpage.action?pageId=2792228606 User-Agent : Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.94 Safari/537.36 Referrer : https://extranet.atlassian.com/pages/resumedraft.action?draftId=2792228606&draftShareId=8e3b3775-7f81-4606-af54-b74f09e27f23 Screen Resolution : 1680 x 1050 User Name : thunguyen Current Dark Features : confluence.view.edit.transition,confluence-inline-comments-resolved,confluence-monitoring.hibernate.enable,federated.search,jirachart.createdvsresolved,file-annotations,confluence.efi.onboarding.rich.space.content,view-file-macro-placeholder,view-file-macro-insert-from-drag-and-drop,show.business.group.in.user.hover,confluence.table.resizable,remove.attachment.button,notification.batch,confluence-inline-comments-rich-editor,blueprint-retrospectives,confluence-table-enhancements.copy-cut-paste-cols,heatmapper,cql.search.screen,clc.quick.create,view-file-thumbnail,confluence-table-enhancements.sticky-headers,jirachart.twodimensional,confluence-table-enhancements.auto-row,nps.survey.inline.dialog,confluence.efi.onboarding.new.templates,total-comment-count,confluence.efi.onboarding.1185.demo-enabled,view-file-macro-convert-to-thumbnail,site-wide.shared-drafts,pdf-preview,blueprint-jirareports,previews.versions,confluence-monitoring.enable,confluence.wrap.macro,previews.conversion-service,editor.ajax.save,content.rank,wiki.macro.disable.antisamy,previews.trigger-all-file-types,view-file-macro-insert-from-exclamation-mark,view-file-thumbnail-polling,jira-placeholder,confluence.request.access.enable,email-tracking,confluence.dark.feature.view-storage,file-notifications,com.atlassian.analytics.auto.whitelist.grow.events,ondemand.marketplace.prototype,file-annotations.likes,site-wide.synchrony,confluence.table.resizable.relative,blueprint-decisions,notification.plugin.api.enabled.com.atlassian.confluence.plugins.sharepage.api.ShareAttachmentEvent,confluence-inline-comments,confluence-inline-comments-dangling-comment,notification.plugin.api.enabled.com.atlassian.confluence.plugins.sharepage.api.ShareContentEvent,notification.plugin.api.enabled.com.atlassian.confluence.plugins.mentions.api.ConfluenceMentionEvent,notification.plugin.api.enabled.com.atlassian.confluence.event.events.security.ForgotPasswordEvent,notification.plugin.api.enabled.com.atlassian.confluence.plugins.tasklist.event.SendTaskEmailEvent,notification.plugin.api.enabled.com.atlassian.confluence.event.events.content.page.async.PageMovedEvent,previews.sharing,notification.plugin.api.enabled.com.atlassian.confluence.plugins.files.notifications.event.FileContentUpdateEvent,notification.plugin.api.enabled.com.atlassian.confluence.event.events.content.attachment.AttachmentBatchUploadCompletedEvent,notification.plugin.api.enabled.com.atlassian.confluence.event.events.content.comment.CommentCreateEvent,notification.plugin.api.enabled.com.atlassian.confluence.efi.emails.events.OnboardingLessUsersEvent,notification.plugin.api.enabled.com.atlassian.confluence.plugins.files.notifications.event.FileContentRemoveEvent,atlassian.aui.raphael.disabled,notification.plugin.api.enabled.com.atlassian.confluence.event.events.content.comment.CommentUpdateEvent,notification.plugin.api.enabled.com.atlassian.confluence.event.events.follow.FollowEvent,notification.plugin.api.enabled.com.atlassian.confluence.event.events.content.page.async.PageEditedEvent,notification.plugin.api.enabled.com.atlassian.confluence.event.events.content.blogpost.BlogPostCreateEvent,notification.plugin.api.enabled.com.atlassian.confluence.plugins.inlinecomments.events.InlineCommentResolveEvent,notification.plugin.api.enabled.com.atlassian.confluence.event.events.like.LikeCreatedEvent,notification.plugin.api.enabled.com.atlassian.confluence.plugins.inlinecomments.events.InlineCommentCreateEvent,previews.sharing.pushstate,notification.plugin.api.enabled.com.atlassian.confluence.event.events.content.blogpost.BlogPostUpdateEvent,notification.plugin.api.enabled.com.atlassian.confluence.event.events.content.page.async.PageCreatedEvent,notification.plugin.api.enabled.com.atlassian.confluence.plugins.files.notifications.event.FileContentMentionUpdateEvent,notification.plugin.api.enabled.com.atlassian.confluence.efi.emails.events.OnboardingNoSpaceCreatedEvent,notification.plugin.api.enabled.com.atlassian.confluence.plugins.hipchat.api.events.HipChatUserMapped,quick-reload-inline-comments-flags,notification.plugin.api.enabled.com.atlassian.confluence.event.events.content.blogpost.BlogPostMovedEvent SpaceTheme : theme-default aui-layout aui-theme-default VersionNumber : 5.10.0-m03