public MessageSecurityMetadataSourceRegistry expressionHandler(SecurityExpressionHandler<Message<Object>> expressionHandler) {
		Assert.notNull(expressionHandler, "expressionHandler cannot be null");
		this.expressionHandler = expressionHandler;
		return this;
	}
public MessageSecurityMetadataSourceRegistry expressionHandler(SecurityExpressionHandler<Message<Object>> expressionHandler) {
		Assert.notNull(expressionHandler, "expressionHandler cannot be null");
		this.expressionHandler = expressionHandler;
		return this;
	}
public MessageSecurityMetadataSourceRegistry expressionHandler ( SecurityExpressionHandler < Message < Object > > expressionHandler ) { Assert . notNull ( expressionHandler , "expressionHandler cannot be null" ) ; this . expressionHandler = expressionHandler ; return this ; }
The {@link SecurityExpressionHandler} to be used. The
default is to use {@link DefaultMessageSecurityExpressionHandler}.

@param expressionHandler the {@link SecurityExpressionHandler} to use. Cannot be null.
@return the {@link MessageSecurityMetadataSourceRegistry} for further
customization.
The { @link SecurityExpressionHandler } to be used . The default is to use { @link DefaultMessageSecurityExpressionHandler } .