Bug 103927 [build path] External jar Dialog cannot set both Javadoc Location and Java Source Attachment in one iteration
Add an external jar to the project. From the context menu of the jar select properties. Select Javadoc location, browse to the desired location. Select Java Source Attachment. Browse to an external file. Press OK. From the context menu of the jar select properties again. Javadoc location is empty. (At this point it can be entered again without problems)
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/LibrariesWorkbookPage.java
if (key.equals(CPListElement.SOURCEATTACHMENT)) {
			IClasspathEntry result= BuildPathDialogAccess.configureSourceAttachment(getShell(), selElement.getClasspathEntry());
			if (result != null) {
				selElement.setAttribute(CPListElement.SOURCEATTACHMENT, result.getSourceAttachmentPath());
				attributeUpdated(selElement);
				fLibrariesList.refresh(elem);
				fLibrariesList.update(selElement); 
				fClassPathList.refresh(); 
			}
		} else if (key.equals(CPListElement.JAVADOC)) {
			String initialLocation= (String) selElement.getAttribute(CPListElement.JAVADOC);
			
			String elementName= new CPListLabelProvider().getText(selElement);
			try {
				URL url= initialLocation != null ? new URL(initialLocation) : null;
				URL[] result= BuildPathDialogAccess.configureJavadocLocation(getShell(), elementName, url);
				if (result != null) {
					URL newURL= result[0];
					selElement.setAttribute(CPListElement.JAVADOC, newURL != null ? newURL.toExternalForm() : null);
					attributeUpdated(selElement);
					fLibrariesList.refresh(elem);
					fClassPathList.dialogFieldChanged(); 
				}
			} catch (MalformedURLException e) {
				
			}
		} else if (key.equals(CPListElement.ACCESSRULES)) {
			AccessRulesDialog dialog= new AccessRulesDialog(getShell(), selElement, fCurrJProject, fPageContainer != null);
			int res= dialog.open();
			if (res == Window.OK || res == AccessRulesDialog.SWITCH_PAGE) {