value truncated in error messages

[jmandel]

Bug

When an invalid displayLanguage is provided, the error message shows a truncated value. displayLanguage=xx is reported as 'x' in the error. The parser appears to read only the first character of the language tag.

Repro

curl -s 'https://tx-dev.fhir.org/r4/CodeSystem/$validate-code?url=http://snomed.info/sct&code=80146002&displayLanguage=xx' \
  -H 'Accept: application/fhir+json' | jq '.parameter[] | select(.name=="message") | .valueString'
# Error message refers to 'x' instead of 'xx'