protected String getContent( TopicExpression topicExpr )
throws TopicExpressionException
{
if ( !( topicExpr.getContent() instanceof String ) )
{
throw new TopicExpressionException( "This evaluator requires the TopicExpression content to be a String." );
}
String expr = (String) topicExpr.getContent();
if ( StringUtils.isEmpty( expr ) || !StringUtils.containsNone( expr, " \t\n\r\f" ) )
{
throw new InvalidTopicExpressionException( "Full topic expression contains whitespace." );