How to remove the superfluous empty line before the list environment?

Question

I want to put the section title in the left margin using titlesec. However, it results to a superfluous empty line when using list environment. How should I remove it without using vspace?

Minimal example:

\documentclass{article}

\usepackage{geometry}
\geometry{
  a4paper,
  top=2cm,
  bottom=2cm,
  left=4.5cm,
  right=1.5cm,
}

\usepackage{titlesec}
\titleformat{\section}[leftmargin]{\large\scshape\sffamily}{}{0cm}{}
\titlespacing{\section}{2.5cm}{2ex}{0.5cm}

\usepackage{enumitem}

\usepackage{mwe}

\begin{document}

\section{Section A}

This line is aligned with the section title.

\blindtext

\section{Section B}

\begin{itemize}[nosep]
  \item This line is not aligned with the section title.
\end{itemize}

\end{document}

Answer 1

You can change the beginning of itemize like this:

\begin{itemize}[nosep,before=\leavevmode\vspace*{-1\baselineskip}] 

I added option showframe and a little bit text to get rid of possible problems caused by \blindtext direct before \begin{itemize}.

Please see the following MWE

\documentclass{article}

\usepackage{geometry}
\geometry{%
  a4paper,
  top=2cm,
  bottom=2cm,
  left=4.5cm,
  right=1.5cm,
  showframe % <=========================================================
}

\usepackage{titlesec}
\titleformat{\section}[leftmargin]{\large\scshape\sffamily}{}{0cm}{}
\titlespacing{\section}{2.5cm}{2ex}{0.5cm} 

\usepackage{enumitem}
\usepackage{blindtext}


\begin{document}

\section{Section A}

This line is aligned with the section title.

\blindtext

Some text to get rid of blindtext.

\section{Section B}
%This is some text. 

\begin{itemize}[nosep,before=\leavevmode\vspace*{-1\baselineskip}] % [nosep]
  \item This line is not aligned with the section title.
  \item second item. second item. second item. second item. second item. 
     second item. second item. second item. second item. second item. second item. 
\end{itemize}

\end{document}

and the result:

Answer 2

Here is a solution with enumitem:

\documentclass{article}

\usepackage{geometry}
\geometry{
  a4paper,
  vmargin=2cm,
  left=4.5cm,
  right=1.5cm,
}

\usepackage{titlesec}
\titleformat{\section}[leftmargin]{\large\scshape\sffamily}{}{0cm}{}
\titlespacing{\section}{2.5cm}{2ex}{0.5cm}

\usepackage{enumitem}

\usepackage{mwe}

\begin{document}

\section{Section A}

This line is aligned with the section title.

\blindtext

\section{Section B}

\begin{itemize}[topsep=0pt, before =\leavevmode\vspace*{-\baselineskip}]
  \item This line is aligned with the section title.
\end{itemize}

\end{document}