How to determine whether a field is empty or null

[uglyliu]

When I test on this website https://playground.vrl.dev/, my configuration is as follows, and I always get an error

.t1 = "-"
.t2 = 3

if is_nullish(.t1) || is_empty(.t1) {
  .t3 = 0
} else {
   .t3 = .t2 - .t1
}

The error is reported as follows

error[E103]: unhandled fallible assignment
  ┌─ :9:10
  │
9 │    .t3 = .t2 - .t1
  │    ----- ^^^^^^^^^ this expression is fallible because at least one argument's type cannot be verified to be valid
  │    │
  │    or change this to an infallible assignment:
  │    .t3, err = .t2 - .t1
  │
  = see documentation about error handling at https://errors.vrl.dev/#handling
  = see functions characteristics documentation at https://vrl.dev/expressions/#function-call-characteristics
  = learn more about error code 103 at https://errors.vrl.dev/103
  = see language documentation at https://vrl.dev
  = try your code in the VRL REPL, learn more at https://vrl.dev/examples

Then I changed the configuration to look like this，it‘s ok

.t1 = "-"
.t2 = 3

if is_nullish(.t1) || is_empty(.t1) {
  .t3 = 0
} else {
   .t3, err = .t2 - .t1
}

Then I changed the configuration to the following

.t1 = 2
.t2 = 3

if is_nullish(.t1) || is_empty(.t1) {
  .t3 = 0
} else {
   .t3, err = .t2 - .t1
}

The error is reported as follows

error[E110]: invalid argument type
  ┌─ :6:32
  │
6 │ if is_nullish(.t1) || is_empty(.t1) {
  │                                ^^^
  │                                │
  │                                this expression resolves to the exact type integer
  │                                but the parameter "value" expects one of string, array or object
  │
  = learn more about error code 110 at https://errors.vrl.dev/110
  = see language documentation at https://vrl.dev
  = try your code in the VRL REPL, learn more at https://vrl.dev/examples

How should this be solved? Thank you very much

[jszwedko]

is_empty doesn't work with integers. What do you want to check for t1? That it is non-zero?

[uglyliu]

The t1 field may be empty or '-'

[jszwedko]

I would just stick with is_nullish then which also detects empty strings.

[uglyliu]

When I change to this configuration, .t3,err = .t2 - .t1 will prompt. I don’t know when to add err and when not to add it.

.t1 = 1
.t2 = 2

if is_nullish(.t1) || is_nullish(.t2) {
   .t3 = 0
} else {
   .t3,err = .t2 - .t1
}

The error is

error[E104]: unnecessary error assignment
   ┌─ :10:8
   │
10 │    .t3,err = .t2 - .t1
   │    --- ^^^   --------- because this expression can't fail
   │    │   │
   │    │   this error assignment is unnecessary
   │    use: .t3 = .t2 - .t1