Orquesta workflow ctx().get() throws a YAQL error

[markcrobinson]

SUMMARY

An Orquesta workflow doesn't seem to allow the use of ctx().get(varname,default_val) for attempting to retrieve variables that may not exist from the runtime context.
@nzlosh asked me to open this bug (on the Slack #community channel

STACKSTORM VERSION

st2 3.1.0, on Python 2.7.5
Single box

OS, environment, install method

RHEL 7.6 scripted install

Steps to reproduce the problem

Create and run a workflow using this gist:
https://gist.github.com/markcrobinson/50aeda08afc9b6222983344df9ec7f8c

Expected Results

message1 and message2 contain the contents of the variables published in the tasks
message3 contains the default value ("See ya")

Actual Results

Running the workflow throws a YAQL error for each of the three output statements:

$ st2 run testing.test-ctx-get
.
id: 5e4558b7103007aab0b8bf7b
action.ref: testing.test-ctx-get
parameters: None
status: failed
start_timestamp: Thu, 13 Feb 2020 14:09:59 UTC
end_timestamp: Thu, 13 Feb 2020 14:10:00 UTC
result:
  errors:
  - expression: <% ctx().get("start_message","Hello world") %>
    language: yaql
    message: Variable "get" is referenced before assignment.
    schema_path: properties.output
    spec_path: output[0]
    type: context
  - expression: <% ctx().get("stop_message","Goodbye") %>
    language: yaql
    message: Variable "get" is referenced before assignment.
    schema_path: properties.output
    spec_path: output[1]
    type: context
  - expression: <% ctx().get("nonexistent","See ya") %>
    language: yaql
    message: Variable "get" is referenced before assignment.
    schema_path: properties.output
    spec_path: output[2]
    type: context
  output: null

isDict(ctx()) returns true
Assigning ctx() into a variable forces it to be a dictionary. @nzlosh game me this workaround:

<% let(x => ctx()) -> $x.get(var, "default") %>

[m4dcoder]

Looks like orquesta is confusing the dict methods as variables during validation.