Groovy Expression to a Default Value

Content

Hi,

i trying to load a Default value for a flexfield using the Groovy Expression, but i don't know if i use the expression right or if have a documentation to how use this expressions. 

I'm try this: 

if (FlexParam?.CategoryId == 300000038787032 || FlexParam?.CategoryId == 300000038786978) {
  return "Use"
} else {
  return "Don't Use"
}

 

This is right? I can do that? I can too disable the input?

When i customize the inputs, i have some configurations to do. One this is construct some logical to the input, how i get the CategoryId of the line and make a logic to Hide or Show the field?