Build warning of non-void return from function (AtomicString)

[17650/23650] /usr/bin/x86_64-pc-linux-gnu-g++ -MMD -MF obj/third_party/blink/renderer/core/css/css_9/style_environment_variables.o.d -DV8_DEPRECATION_WARNINGS -DUSE_UDEV -DUSE_AURA=1 -DUSE_NSS_CERTS=1 -DUSE_OZONE=1 -DNO_TCMALLOC -DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD -DSAFE_BROWSING_DB_LOCAL -DOFFICIAL_BUILD -DCHROMIUM_BUILD -DFIELDTRIAL_TESTING_ENABLED -DTOOLKIT_QT -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -DNDEBUG -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -DBLINK_CORE_IMPLEMENTATION=1 -DGL_GLEXT_PROTOTYPES -DUSE_GLX -DUSE_EGL -DBLINK_IMPLEMENTATION=1 -DINSIDE_BLINK -DU_USING_ICU_NAMESPACE=0 -DU_ENABLE_DYLOAD=0 -DU_STATIC_IMPLEMENTATION -DICU_UTIL_DATA_IMPL=ICU_UTIL_DATA_FILE -DUCHAR_TYPE=uint16_t -DGOOGLE_PROTOBUF_NO_RTTI -DGOOGLE_PROTOBUF_NO_STATIC_INITIALIZER -DHAVE_PTHREAD -DSK_IGNORE_LINEONLY_AA_CONVEX_PATH_OPTS -DSK_HAS_PNG_LIBRARY -DSK_HAS_WEBP_LIBRARY -DSK_HAS_JPEG_LIBRARY -DSK_SUPPORT_GPU=1 -DSK_GPU_WORKAROUNDS_HEADER=\"gpu/config/gpu_driver_bug_workaround_autogen.h\" -DWTF_USE_WEBAUDIO_FFMPEG=1 -DSUPPORT_WEBGL2_COMPUTE_CONTEXT=1 -DWTF_USE_DEFAULT_RENDER_THEME=1 -DUSE_SYSTEM_LIBJPEG -DWEBRTC_NON_STATIC_TRACE_EVENT_HANDLERS=0 -DGTEST_RELATIVE_PATH -DWEBRTC_CHROMIUM_BUILD -DWEBRTC_POSIX -DWEBRTC_LINUX -DABSL_ALLOCATOR_NOTHROW=1 -DNO_MAIN_THREAD_WRAPPING -DUSE_SYSTEM_ZLIB=1 -Igen -I../../3rdparty/chromium -Igen -Igen -Igen -Igen -I../../3rdparty/chromium/third_party/khronos -I../../3rdparty/chromium/gpu -I../../3rdparty/chromium/third_party/libyuv/include -Igen -Igen -Igen -Igen -Igen -Igen -Igen -I../../3rdparty/chromium/third_party/ced/src -I../../3rdparty/chromium/third_party/icu/source/common -I../../3rdparty/chromium/third_party/icu/source/i18n -I../../3rdparty/chromium/third_party/protobuf/src -I../../3rdparty/chromium/third_party/protobuf/src -Igen/protoc_out -I../../3rdparty/chromium/third_party/boringssl/src/include -I../../3rdparty/chromium/skia/config -I../../3rdparty/chromium/skia/ext -I../../3rdparty/chromium/third_party/skia/include/c -I../../3rdparty/chromium/third_party/skia/include/config -I../../3rdparty/chromium/third_party/skia/include/core -I../../3rdparty/chromium/third_party/skia/include/effects -I../../3rdparty/chromium/third_party/skia/include/encode -I../../3rdparty/chromium/third_party/skia/include/gpu -I../../3rdparty/chromium/third_party/skia/include/images -I../../3rdparty/chromium/third_party/skia/include/lazy -I../../3rdparty/chromium/third_party/skia/include/pathops -I../../3rdparty/chromium/third_party/skia/include/pdf -I../../3rdparty/chromium/third_party/skia/include/pipe -I../../3rdparty/chromium/third_party/skia/include/ports -I../../3rdparty/chromium/third_party/skia/include/utils -I../../3rdparty/chromium/third_party/skia/src/gpu -I../../3rdparty/chromium/third_party/skia/src/sksl -I../../3rdparty/chromium/third_party/angle/include -I../../3rdparty/chromium/third_party/angle/src/common/third_party/base -Igen/angle -I../../3rdparty/chromium/v8/include -Igen/v8/include -I../../3rdparty/chromium/third_party/webrtc_overrides -I../../3rdparty/chromium/third_party/webrtc -I../../3rdparty/chromium/third_party/iccjpeg -I../../3rdparty/chromium/third_party/ots/include -I../../3rdparty/chromium/v8/include -Igen/v8/include -fno-strict-aliasing --param=ssp-buffer-size=4 -fstack-protector -funwind-tables -fPIC -pipe -pthread -m64 -Wall -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -Wno-unused-local-typedefs -Wno-maybe-uninitialized -Wno-deprecated-declarations -fno-delete-null-pointer-checks -Wno-comments -Wno-dangling-else -Wno-packed-not-aligned -Wno-missing-field-initializers -Wno-unused-parameter -fno-omit-frame-pointer -fvisibility=hidden -O2 -fno-ident -fdata-sections -ffunction-sections -g0 -isystem../../../../../../../../../../usr/include/nss -isystem../../../../../../../../../../usr/include/nspr -isystem ../../3rdparty/chromium/third_party/abseil-cpp -isystem../../../../../../../../../../usr/include/libpng16 -isystem../../../../../../../../../../usr/include/libxml2 -isystem../../../../../../../../../../usr/include/libxml2 -std=gnu++14 -Wno-narrowing -Wno-attributes -Wno-class-memaccess -Wno-subobject-linkage -fno-exceptions -fno-rtti -fvisibility-inlines-hidden -c ../../3rdparty/chromium/third_party/blink/renderer/core/css/style_environment_variables.cc -o obj/third_party/blink/renderer/core/css/css_9/style_environment_variables.o
../../3rdparty/chromium/third_party/blink/renderer/core/css/style_environment_variables.cc: In static member function ‘static const WTF::AtomicString blink::StyleEnvironmentVariables::GetVariableName(blink::UADefinedVariable)’:
../../3rdparty/chromium/third_party/blink/renderer/core/css/style_environment_variables.cc:70:1: warning: control reaches end of non-void function [-Wreturn-type]
   70 | }
      | ^