Describe the Bug

See this example:
https://nikku.github.io/feel-playground/?e=string%28obj.number%29&c=%7B%0A++%22obj%22%3A+%7B%7D%0A%7D&t=expression&st=true

Steps to Reproduce

Expected Behavior

Seems like "number" property is treated as a function when it's value is unset in provided context

Environment

• Host (Browser/Node version), if applicable: any
• OS: any
• Library version: latest