Ast fix: condition added in ftd::ast::VariableValue

[Arpita-Jaiswal]

Earlier the following code was not working:

-- optional string name:


-- rendered:

-- rendered.text:

Hello

-- rendered.uis:

-- ftd.text: Hello

-- ftd.code:
if: {name != NULL}
text: $name
lang: ftd

-- end: rendered.uis

-- end: rendered






-- component rendered:
body text:
children uis:

-- ftd.column:

-- ftd.text: $rendered.text

-- ftd.column:
children: $rendered.uis

-- end: ftd.column

-- end: ftd.column

-- end: rendered

The generated ast didn't contain condition if: {name != NULL}. This PR fix this issue.