How to create beamer blocks with empty title

Here is a minimal working example on how to create such a block:

% Blocks without title in Beamer
\documentclass{beamer}

% set a theme to have nice and different blocks
\usetheme{Warsaw}

\begin{document}

\begin{frame}{Blocks without title}
% create the main block
\begin{exampleblock}{Title of the block}
    This is the block with the main contents.
\end{exampleblock}

% create a other blocks, visually separated,
% that continues the contents of the previous block
\begin{exampleblock}{}
    A natural but separated continuation of the previous block.
\end{exampleblock}

\begin{block}{}
    This is a standard block without title.
\end{block}

\begin{alertblock}{}
    This is an alert block without title.
\end{alertblock}
% since no title is specified, it will not appear the title band
\end{frame}
\end{document}

Compiling this code yields: