CMake FetchContent build error

Describe the bug
I'm attempting to switch my project's dependencies over to CMake's FetchContent functionality, but jsoncpp returns a build error. Full disclaimer, I'm just starting to experiment with the FetchContent functionality and I'm not an expert on CMake.

I'm using CMake 3.25.2. The version of CMake that introduced FetchContent_MakeAvailable, which downloads and builds external dependencies, was 3.14.

Here's the error:

λ cmake .
[...]
-- JsonCpp Version: 1.9.5
######################################################
# jsoncpp should not be configured & built in the jsoncpp source directory
# You must run cmake in a build directory.
# For example:
# mkdir jsoncpp-Sandbox ; cd jsoncpp-sandbox
# git clone https://github.com/open-source-parsers/jsoncpp.git # or download & unpack the source tarball
# mkdir jsoncpp-build
# this will create the following directory structure
#
# jsoncpp-Sandbox
#  +--jsoncpp
#  +--jsoncpp-build
#
# Then you can proceed to configure and build
# by using the following commands
#
# cd jsoncpp-build
# cmake ../jsoncpp # or ccmake, or cmake-gui
# make
#
# NOTE: Given that you already tried to make an in-source build
#       CMake have already created several files & directories
#       in your source tree. run 'git status' to find them and
#       remove them by doing:
#
#       cd jsoncpp-Sandbox/jsoncpp
#       git clean -n -d
#       git clean -f -d
#       git checkout --
#
######################################################
CMake Error at _deps/jsoncpp_dep-src/include/PreventInSourceBuilds.cmake:41 (message):
  Quitting configuration
Call Stack (most recent call first):
  _deps/jsoncpp_dep-src/include/PreventInSourceBuilds.cmake:45 (AssureOutOfSourceBuilds)
  _deps/jsoncpp_dep-src/CMakeLists.txt:81 (include)

To Reproduce
Steps to reproduce the behavior:

1. Include the following snippet in a project with a CMakeLists.txt file:

cmake_minimum_required (VERSION 3.14)
[...]
FetchContent_Declare (jsoncpp_dep
	GIT_REPOSITORY https://github.com/open-source-parsers/jsoncpp
	GIT_TAG 5defb4ed1a4293b8e2bf641e16b156fb9de498cc)

FetchContent_MakeAvailable (jsoncpp_dep)

2. Run cmake . in the project directory.

Expected behavior
The project would build as expected.

Desktop (please complete the following information):

• OS: macOS 12.6.3 Monterey
• CMake 3.25.2

Reproduce the issue with the provided CMakeLists.txt snippet and cmake .. Start by reading _deps/jsoncpp_dep-src/include/PreventInSourceBuilds.cmake and the call from CMakeLists.txt at line 81. Done means the FetchContent configuration no longer aborts with the in-source-build error and the project builds as expected.