Is there a LaTeX equivalent symbol to Unicode 'SYMBOL FOR NULL'

If a TeX engine is used with Unicode/OpenType font support, then it is just a matter to find a font that contains the Unicode code point U+2400, e.g.:

% lualatex or xelatex
\documentclass{article}
\usepackage{fontspec}
\begin{document}
\def\test#1{#1:&\fontspec{#1}\symbol{"2400}\\}
\begin{tabular}{l@{ }l}
  \test{FreeMono}
  \test{FreeSans}
  \test{FreeSerif}
  \test{Quivira}% http://www.quivira-font.com/
\end{tabular}
\end{document}

If you are on pdflatex, you can use the ascii package:

\documentclass{article}
\usepackage{ascii}

\begin{document}

Is this it? \NUL

\end{document}

You can also input the symbol directly as Unicode, so the code can be portable to XeLaTeX or LuaLaTeX.

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{ascii}
\usepackage{newunicodechar}

\newunicodechar{␀}{\NUL}

\begin{document}

Is this it? ␀

\end{document}

With XeLaTeX or LuaLaTeX and fontspec, find a font with the character and then do like

\documentclass{article}
\usepackage{fontspec}
\usepackage{newunicodechar}

\newfontface{\ASCIICONTROLS}{FreeMono} % <--- or another font
\newunicodechar{␀}{{\ASCIICONTROLS ␀}}

\begin{document}

Is this it? ␀

\end{document}

If you wanted it to conform to the current font, both in size and style, you could build your own:

\documentclass[a2]{article}
\usepackage{stackengine,scalerel}
\newcommand\NUL{\scalerel*{$\Shortstack[l]{N \phantom{N}U \phantom{NU}L}$}{X}}
\begin{document}
\LARGE
This is \NUL

\normalsize
This is \NUL

\itshape
This is \NUL

\upshape\ttfamily
This is \NUL

\end{document}

If one wanted the symbol always in bold, for clarity, then

\newcommand\NUL{\scalerel*{$\bfseries\Shortstack[l]{N \phantom{N}U \phantom{NU}L}$}{X}}

would remedy that: