Empty item in env field inside c_cpp_properties.json causes error

[schperplata]

Type: LanguageService
Issue Type: Bug

I'm playing around with using VS Code for embedded project. I have created a c_cpp_properties.json file, where I am planing to list all directories and files inside of different "env" fields and than passing this values to "configuration" "includePath", "browse" and "define" fields.

The problem specifically is caused by an empty field, followed by a non empty field, see example below:

{
    "env": {
        ...
        "userDefines": [],
        ...
        "cubeMXDefines": [
            "USE_HAL_DRIVER",
            "STM32F078xx"
        ],
        ...
    },
    "configurations": [
        {
            ...
            "defines": [
                "${userDefines}",
                "${cubeMXDefines}"
            ],
            ...
        }
    ],
    "version": 4
}

As you can see, userDefines field is empty, while cubeMXDefines in not. While editing main.c for example, I get an error in problems tab:

If I write anything into userDefines field, Intellisense works as expected.
Is there something I am missing, or is this a bug (not handled empty env field)?

VS Code version: Code 1.27.2 (f46c4c469d6e6d8c46f268d1553c5dc4b475840f, 2018-09-12T16:17:45.060Z)
OS version: Windows_NT x64 10.0.17134

System Info

Item	Value
CPUs	Intel(R) Core(TM) i5-2520M CPU @ 2.50GHz (4 x 2494)
GPU Status	2d_canvas: enabled checker_imaging: disabled_off flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on native_gpu_memory_buffers: disabled_software rasterization: enabled video_decode: enabled video_encode: enabled webgl: enabled webgl2: enabled
Memory (System)	7.95GB (3.16GB free)
Process Argv	C:\Users\domen\AppData\Local\Programs\Microsoft VS Code\Code.exe
Screen Reader	no
VM	0%

Extensions (6)

Extension	Author (truncated)	Version
bracket-pair-colorizer	Coe	1.0.60
CppSnippets	har	0.0.13
cortex-debug	mar	0.1.21
python	ms-	2018.8.0
cpptools	ms-	0.18.1
debug	web	0.22.0

[bobbrow]

The replacement logic is using a "falsy" check to see if a replacement should be made. It probably needs to handle an empty array separately.

[sean-mcmanus]

This empty array environment variable bug is fixed in 0.19.0.