Add String Literal in where parser

[daewon]

Where parser do not provide string literal Because parser cannot compare property value with empty string. and it can be ambiguous between property name or property value

Label meta Info

name: "address", dataType: "string", defaultValue: ""

ex) filter out empty string

as is
where address != 

to be
where address != ''

ex) Ambiguous with property name

as is
where address=address

to be 
whee address='address'