bug: reading an empty json object into a Map task output produces a ValueError

[ahvigil]

On miniwdl v1.12.1 running the following minimal workflow example:

version development

workflow demo {
    call echo
}

task echo {
    command <<<
        echo '{}' > output.json
    >>>

    output {
        Map[String, String] output_map = read_json("output.json")
    }
}

produces the following task runtime error during execution

Traceback (most recent call last):
  File ".../python3.12/site-packages/WDL/runtime/task.py", line 213, in run_local_task
    outputs = link_outputs(
              ^^^^^^^^^^^^^
  File ".../python3.12/site-packages/WDL/runtime/task.py", line 891, in link_outputs
    return outputs.map(
           ^^^^^^^^^^^^
  File ".../python3.12/site-packages/WDL/Env.py", line 151, in map
    fb = f(b)
         ^^^^
  File ".../python3.12/site-packages/WDL/runtime/task.py", line 894, in <lambda>
    map_paths(
  File ".../python3.12/site-packages/WDL/runtime/task.py", line 865, in map_paths
    d = int(math.ceil(math.log10(len(v.value))))
                      ^^^^^^^^^^^^^^^^^^^^^^^^
ValueError: math domain error