gst-build lexer error

im trying to build

$ git clone https://gitlab.freedesktop.org/gstreamer/gst-build.git
$ cd gst-build
$ meson build

but get this lexer error

The Meson build system
Version: 0.45.1
Source dir: /home/ubuntu/dev/gst/gst-build
Build dir: /home/ubuntu/dev/gst/gst-build/build
Build type: native build

meson.build:50:15: ERROR: lexer
  ['gstreamer', {'build-hotdoc': true, 'has-plugins': true}],
     ```          ^