Error executing simple task in Ubuntu 18.04

[vics80]

I write a simple task with a simple CSS and when I execute I get this error:

UnhandledPromiseRejectionWarning: SyntaxError: Unexpected token T in JSON

This error is in file node_modules/penthouse/lib/postformatting/index.js:28:28
This line is:

var criticalRules = JSON.parse(cssAstRulesJsonString)

When I print this Json I get this:

[{"declarations":[{"position":{"end":{"column":15,"line":2},"start":{"column":1,"line":2}},"property":"display","type":"declaration","value":"block"}],"position":{"end":{"column":2,"line":3},"start":{"column":1,"line":1}},"selectors":["body"],"type":"rule"}]TypeError: Attempting to change the setter of an unconfigurable property