Getting Empty bollean

[apneduniya]

This is my components/buttons.ftd:

-- component wrapper:
caption title: ;; done
optional string role: ;; F U N C T I O N A L I T Y
optional string link:
optional boolean new-tab:
optional boolean disabled:
optional string $mouse-in:
optional string color: ;;  S T Y L E S
optional string background: ;; background-color
optional integer border-width:
optional string border-color:


;; Main button container
-- ftd.row:
background.solid if { wrapper.background != NULL }: $wrapper.background
background.solid: #E5E5E5
border-width.px if { wrapper.border-width != NULL }: $wrapper.border-width
border-width.px: 1
border-color if { wrapper.border-color != NULL }: $wrapper.border-color
border-color: #9A9A9A
border-radius.px: 4
padding-vertical.px: 2
padding-horizontal.px: 6
overflow: hidden
cursor: pointer 
link if { wrapper.link != NULL && !wrapper.disabled }: $wrapper.link
link if { wrapper.disabled }: #
link: #
;; shadow: $wrapper-shadow

-- ftd.text:
text: $wrapper.title
color if { wrapper.color != NULL }: $wrapper.color
color: #000000


-- end: ftd.row

-- end: wrapper

Code of my index.ftd where I am calling that button component:

-- button.wrapper: Hello Fastn!

---

After doing fastn serve I am getting this error:

fastn-Error: path: /, FTDExecError(InterpreterError(EvalexprError(ExpectedBoolean { actual: Empty })))