LogicApp DotLiquid string empty or null check not working as expected

Question

I'm using liquid templates in an Azure Standard Logic App. I have a null / empty test at the beginning of the file that is behaving differently (and weirdly) to LiquidJS and online liquid playgrounds that I test.

This is the statement:

{% assign itemExists = content.existing != null and content.existing.UID != null and content.existing.UID != "" -%}

then I use it later to generate some GraphQL:

{% if itemExists -%}
    _a0: updateFoo(input: {
        UID: "{{ content.existing.UID }}"
{% else -%}
    _a0: insertFoo(input: {
{% endif -%}

The problem is that UID is an empty string "" and yet it's following the first if path, thereby producing the output:

    _a0: updateFoo(input: {
        UID: ""

I've verified that the UID is an empty string in the logic app run history.

I wrote a quick Jasmine test using exactly the same liquid file, and the same inputs from the logic app, using LiquidJS, and it works fine.

Is this a bug in DotLiquid used in logic apps? If so, how can I get around it?

Update 1:

It only shows when you assign the test to a variable, and then try and use that variable in an if test. This:

{% assign test = "asdf" -%}
{% assign isNullOrWhitespace = test == null or test == empty %}
isNullOrWhitespace is: {{ isNullOrWhitespace }}

Produces isNullOrWhitespace is: asdf instead of the expected isNullOrWhitespace is: false

Update 2:

Bug report here: https://github.com/dotliquid/dotliquid/issues/537

Answer 1

Yes, in Liquid if its even "" a empty string it doesnt consider as null it will consider as not null.

You can use something like below example:

If its not empty:

{% assign test = "Hello Rithwik Bojja" -%}
{% if test != null and test != empty -%}
  The string is not empty and not null. 
    Value:{{test}}
{% else -%}
  The string is empty or null.
{% endif -%}

Output:

If its empty:

{% assign test = "" -%}
{% if test != null and test != empty -%}
  The string is not empty and not null. 
    Value:{{test}}
{% else -%}
  The string is empty or null.
{% endif -%}

Output:

For understanding you can execute code here

Edit:

{% assign test = "Rithwik Bojja" %}
{% assign isItemExists = test | default: nil | unless: empty %}
{% if isItemExists %}
  The string is not empty and not null. 
  Value: {{ test }}
{% else %}
  The string is empty or null.
{% endif %}