Non clear syntax error with unclosed var(

[MoOx]

body {
  font-size: var(--fontSize;
}

Give on the playground

TypeError: balanced(...) is undefined

And with cli

cssnext encounters an error:

Cannot read property 'body' of undefined

    at resolveValue (/Users/MoOx/Sync/Development/cssnext/playground/node_modules/cssnext/node_modules/postcss-custom-properties/index.js:96:66)
    at /Users/MoOx/Sync/Development/cssnext/playground/node_modules/cssnext/node_modules/postcss-custom-properties/index.js:62:23
    at /Users/MoOx/Sync/Development/cssnext/playground/node_modules/cssnext/node_modules/postcss/lib/container.js:402:30
    at Rule.Container.each (/Users/MoOx/Sync/Development/cssnext/playground/node_modules/cssnext/node_modules/postcss/lib/container.js:88:20)
    at Rule.Container.WithDecls.constructor$1.eachDecl (/Users/MoOx/Sync/Development/cssnext/playground/node_modules/cssnext/node_modules/postcss/lib/container.js:400:21)
    at /Users/MoOx/Sync/Development/cssnext/playground/node_modules/cssnext/node_modules/postcss/lib/container.js:331:36
    at Root.Container.each (/Users/MoOx/Sync/Development/cssnext/playground/node_modules/cssnext/node_modules/postcss/lib/container.js:88:20)
    at Root.Container.WithRules.constructor$0.eachDecl (/Users/MoOx/Sync/Development/cssnext/playground/node_modules/cssnext/node_modules/postcss/lib/container.js:329:21)
    at /Users/MoOx/Sync/Development/cssnext/playground/node_modules/cssnext/node_modules/postcss-custom-properties/index.js:55:11
    at PostCSS.process (/Users/MoOx/Sync/Development/cssnext/playground/node_modules/cssnext/node_modules/postcss/lib/postcss.js:34:28)

[MoOx]

Closed by d9a5364