Bug 140542 label can't be displayed without resource file or unmatched key
Steps to reproduce: 1.New a report, add a lable with text "aaa" 2.Add a resource file for the report, set key to "key1", value to "actuate", apply the value to the label 3.Clear the resource file in Property Editor->General->Resource File (or change the key to "abc") 4.Preview the report Expected result: 1.Display label text "aaa" on preview or 2.Give a warning message to say resource file is not found or unmatched key Actual result: Nothing displays on preview
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/Module.java
* 
	 * @return a list of user-defined message keys.
	 */
	public List getMessageKeys( )
	{
		Set keys = new LinkedHashSet( );
		String[] transKeys = translations.getResourceKeys( );
		if ( transKeys != null )
		{
			for ( int i = 0; i < transKeys.length; i++ )
				keys.add( transKeys[i] );
		}
		
		
		String baseName = getStringProperty( this, INCLUDE_RESOURCE_PROP );
		if ( baseName == null )
			return new ArrayList( keys );
		keys.addAll( BundleHelper.getHelper( this, baseName ).getMessageKeys(
				ThreadResources.getLocale( ) ) );
		return new ArrayList( keys );
	}
	/**
	 * Checks if the file with <code>fileName</code> exists. The search steps
	 * are described in {@link #findResource(String, int)}.
	 * 
	 * @param fileName
	 *            the file name to check
	 * @param fileType
	 *            the file type
	 * @return true if the file exists, false otherwise.