Missing and Bad Anchor in Help Browser throws NPE

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In De:Help/Concepts/Object, first paragraph, the link Linien aims formerly aimed to the anchor #WaysAnchor. That anchor is intentionally missing for the purpose of this report. Clicking the link will throw the Null Pointer Exception shown below. Anchors were last dealt with in #15985.

Additionally the same NPE occurs when the anchor is created with [=#Myanchor] and has no content inside the brackets. Trac recommends this in WikiFormatting#SettingAnchors. Trac generates the HTML code <span class="wikianchor" id="Myanchor"></span> which is fine for common browsers. But not for our Help system.

URL:https://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2019-02-12 22:29:23 +0100 (Tue, 12 Feb 2019)
Build-Date:2019-02-13 02:30:51
Revision:14786
Relative:URL: ^/trunk

Identification: JOSM/1.5 (14786 de) Windows 7 64-Bit
OS Build number: Windows 7 Professional (7601)
Memory Usage: 183 MB / 247 MB (14 MB allocated, but free)
Java version: 1.8.0_172-ea-b03, Oracle Corporation, Java HotSpot(TM) Client VM
Screen: \Display0 1280x1024
Maximum Screen Size: 1280x1024
Program arguments: [--trace]

Plugins:
+ PicLayer (34867)
+ apache-commons (34506)
+ ejml (34389)
+ geotools (34513)
+ jaxb (34678)
+ jts (34524)
+ opendata (34867)
+ utilsplugin2 (34867)

Last errors/warnings:
- W: No configuration settings found.  Using hardcoded default values for all pools.
- E: Handled by bug report queue: java.lang.NullPointerException

OSM API: https://api06.dev.openstreetmap.org/api


=== REPORTED CRASH DATA ===
BugReportExceptionHandler#handleException:
No data collected.

Warning issued by: BugReportExceptionHandler#handleException

=== STACK TRACE ===
Thread: AWT-EventQueue-0 (15) of main
java.lang.NullPointerException
	at org.openstreetmap.josm.gui.help.HelpBrowser$HyperlinkHandler.scrollToElementWithId(HelpBrowser.java:582)
	at org.openstreetmap.josm.gui.help.HelpBrowser$HyperlinkHandler.hyperlinkUpdate(HelpBrowser.java:635)
	at javax.swing.JEditorPane.fireHyperlinkUpdate(Unknown Source)
	at javax.swing.text.html.HTMLEditorKit$LinkController.activateLink(Unknown Source)
	at javax.swing.text.html.HTMLEditorKit$LinkController.mouseClicked(Unknown Source)
	at java.awt.AWTEventMulticaster.mouseClicked(Unknown Source)
	at java.awt.Component.processMouseEvent(Unknown Source)
	at javax.swing.JComponent.processMouseEvent(Unknown Source)
	at java.awt.Component.processEvent(Unknown Source)
	at java.awt.Container.processEvent(Unknown Source)
	at java.awt.Component.dispatchEventImpl(Unknown Source)
	at java.awt.Container.dispatchEventImpl(Unknown Source)
	at java.awt.Component.dispatchEvent(Unknown Source)
	at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
	at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
	at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
	at java.awt.Container.dispatchEventImpl(Unknown Source)
	at java.awt.Window.dispatchEventImpl(Unknown Source)
	at java.awt.Component.dispatchEvent(Unknown Source)
	at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
	at java.awt.EventQueue.access$500(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
	at java.awt.EventQueue$4.run(Unknown Source)
	at java.awt.EventQueue$4.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
	at java.awt.EventQueue.dispatchEvent(Unknown Source)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.run(Unknown Source)

[Don-vip]

In 14807/josm:

fix #17338 - NPE

[Hb---]

Verified.