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/SourceAttachmentBlock.java
return fEntry.getEntryKind() == IClasspathEntry.CPE_VARIABLE;
	}
	
	
	/**
	 * Gets the source attachment path chosen by the user
	 */
	public IPath getSourceAttachmentPath() {
		if (fFileNameField.getText().length() == 0) {
			return null;
		}
		return getFilePath();
	}
	/**
	 * Gets the source attachment root chosen by the user
	 * Returns null to let JCore automatically detect the root.
	 */
	public IPath getSourceAttachmentRootPath() {
		return null;
	}
	
	public IClasspathEntry getNewEntry() {
		CPListElement elem= CPListElement.createFromExisting(fEntry, fProject);
		elem.setAttribute(CPListElement.SOURCEATTACHMENT, getSourceAttachmentPath());
		return elem.getClasspathEntry();
	}
		
	/**
	 * Creates the control
	 */