[Tex/LaTex] Define quotation environment without indentation of the first paragraph

Question

I want to have a quotation environment that does not indent the first paragraph.

\documentclass{scrbook} 

\begin{document}

\makeatletter
\renewenvironment{quotation}
           {\list{}{\listparindent 1.5em%
                    \itemindent    \listparindent
                    \rightmargin \leftmargin
                    \parsep        \z@ \@plus\p@}%
            \item\relax}
           {\endlist}
\makeatother

This is normal text. This is normal text. This is normal text.
This is normal text. This is normal text. 
\begin{quotation}

This is a sentence that is devoid of any meaning. It should not be indented.

This ia another sentence. It should be indented. The other one shouldn't.
Some more text here. Some more text here. Some more text here. Some more text here. 

\end{quotation}
This again normal text. This again normal text. This again normal text.
This again normal text.

\end{document}

(A separate question would be how the environment can be modified so that the quote is not indented at the righthand side but instead aligned with the normal text.)

Answer 1

\documentclass{scrbook} 

\begin{document}

\makeatletter
\renewenvironment{quotation}
           {\list{}{\listparindent 1.5em%
                    %\itemindent    \listparindent
                    %\rightmargin \leftmargin
                    \parsep        \z@ \@plus\p@}%
            \item\relax}
           {\endlist}
\makeatother

This is normal text. This is normal text. This is normal text.
This is normal text. This is normal text. 
\begin{quotation}

This is a sentence that is devoid of any meaning. It should not be indented.

This ia another sentence. It should be indented. The other one shouldn't.
Some more text here. Some more text here. Some more text here. Some more text here. 

\end{quotation}
This again normal text. This again normal text. This again normal text.
This again normal text.

\end{document}

The first % stops the first para indenting, the second % stops the right margin being changed.