Runtime error with gltf 2.0 file without texture

[gunmiosb]

Using more than one viewer and loading the same gltf 2.0 file without textures on both leads to this error:

[Cesium WebGL] Fragment shader compile log: ERROR: 0:? : '' : syntax error

[Cesium WebGL] Fragment shader translation failed.
An error occurred while rendering.  Rendering has stopped.
undefined
RuntimeError: Fragment shader failed to compile.  Compile log: ERROR: 0:? : '' : syntax error

Error
    at new RuntimeError (https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:4456:19)
    at createAndLinkProgram (https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:95099:23)
    at initialize (https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:95320:23)
    at ShaderProgram.get (https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:94982:17)
    at getAttributeLocations (https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:151990:47)
    at https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:152204:42
    at Function.ForEach.meshPrimitive (https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:140447:29)
    at https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:152201:21
    at Function.ForEach.object (https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:140257:29)
    at Function.ForEach.topLevel (https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:140276:24)

The error occurred after updating from 1.45 to 1.56.1

Here is a Sandcastle example of the Problem based on the 3D Models example:
Sandcastle

[hpinkos]

Thanks @gunmiosb, this is a known issue #7688
I'll tag you in that issue so we can notify you when it's fixed. If it's not fixed in the May release, it should be fixed for June.