Three.js: Disabling casting shadows on one from multiple lights crashes the renderer

Description of the problem

Given a scene that contains multiple light sources, disabling casting shadows on only one of the lights will result with renderer crashing.

StackTrace:

three.js:16521 Uncaught TypeError: Cannot read property 'toArray' of undefined
    at flatten (three.js:16521)
    at PureArrayUniform.setValueM4Array [as setValue] (three.js:16999)
    at Function.WebGLUniforms.upload (three.js:17248)
    at setProgram (three.js:25307)
    at WebGLRenderer.renderBufferDirect (three.js:24041)
    at renderObject (three.js:24802)
    at renderObjects (three.js:24772)
    at WebGLRenderer.render (three.js:24549)
    at render ((index):111)

This problem started occurring from version r108. In r107 the problem does not occur.

Examples:

• jsfiddle (r109, clicking on 'shadows' will crash the renderer)
• jsfiddle (r107, clicking on 'shadows' will work properly)

Three.js version

• [x] r108
• [x] r108
• [ ] r107

Browser

• [x] All of them
• [ ] Chrome
• [ ] Firefox
• [ ] Internet Explorer

OS

• [x] All of them
• [ ] Windows
• [ ] macOS
• [ ] Linux
• [ ] Android
• [ ] iOS