Redundant printing can occur when using null-input

[echlebek]

Describe the bug

When using yq -n with assignment expressions, some expressions can cause the resulting document to be printed more than once.

Version of yq:

$ yq --version
yq (https://github.com/mikefarah/yq/) version v4.44.2

Installed via: go install

Command

$ yq -n '.a.b.c = "foo", .a.b.d = "bar", .a.b.e = "baz"'

Actual behavior

a:
  b:
    c: foo
    d: bar
    e: baz
a:
  b:
    c: foo
    d: bar
    e: baz

Expected behavior

a:
  b:
    c: foo
    d: bar
    e: baz

Additional context
Discovered while using yqlib to build a document dynamically, found a minimal reproduction quite quickly on the yq command-line application. I tried using the -P flag as well to see if that would mitigate it, but it did not.

[mikefarah]

Hey - try using | instead of , (comma is the union operator, collecting multiple yaml nodes together, whereas | takes the output of the LHS and pipes that into the right, building a single document.

[echlebek]

Thanks, is this expected behaviour for the union operator then?