How do I remove / change the footer at certain slides in my theme `.sty` file?   
I basically want to avoid using `\setbeamertemplate{footline}{}` in my `.tex`. E.g. on the title slide / toc / section slide...   

# Failed attempts

## Using `\newif`
```latex
\newif\ifbeamer@test@title
\beamer@test@titlefalse

\defbeamertemplate*{title page}{test}{
  \beamer@test@titletrue
  <...>
  \beamer@test@titlefalse
}

\defbeamertemplate*{footline}{test}{
  \ifbeamer@test@title
  \else
    <...>
  \fi
}
```

# Minimal Working Example

Here a reduced MWE only considering the title page, however the solution should be general enough such that it can also be used for the table of content / section slides

`cat beamerthemetest.sty`
```latex
\mode<presentation>
%% goes to inner theme
\defbeamertemplate*{title page}{test}
{
	\beamer@test@titletrue
	{
	  \vspace{42pt}
	  \begin{beamercolorbox}{title}
	    \usebeamerfont{title}\inserttitle
	      \ifx\insertsubtitle\@empty
	      \else
	      \par\usebeamerfont{subtitle}\insertsubtitle
	      \fi
	  \end{beamercolorbox}
	  \begin{beamercolorbox}{author}
	    \usebeamerfont{author}\insertauthor
	  \end{beamercolorbox}
  }
  \beamer@test@titlefalse
}

%% goes to outer theme

\defbeamertemplate*{footline}{test}
{
	  \begin{beamercolorbox}[wd=\paperwidth, dp=1mm, ht=3.5mm
	                         , leftskip=1mm, rightskip=1mm
	                        ]{footline}%
	    \usebeamerfont{title in head/foot}%

	    \makebox[240pt][l]{
	      \insertshorttitle\ - \insertsectionhead\ %
	      \ifx\insertsubsectionhead\@empty\relax\else%
	      - \insertsubsectionhead%
	      \fi
	      }
	    \hfill\makebox[20pt][r]{\insertframenumber/\inserttotalframenumber}%
	  \end{beamercolorbox}%
  \fi
}

\mode<all>

```

with the `test.tex`
```latex
\documentclass[aspectratio=169]{beamer}
\usetheme{test}
\author{whoami} 
\title{title}

\begin{document}
\maketitle

\section{abc}
\begin{frame}{abc}
cde
\end{frame}	
\end{document}
```