Determine why some Axe result fields may be empty

[pomerantsev]

node.failureSummary and violation.impact may be empty, according to axe-core types. Is this so? If it is, when can they be empty, and what (if anything) should I do to guard Accented from these empty values?

• accented/packages/accented/src/utils/transform-violations.ts

  Line 47 in 525a622

  description: node.failureSummary ?? violation.description,

• accented/packages/accented/src/utils/transform-violations.ts

  Line 49 in 525a622

  impact: violation.impact ?? null,

[pomerantsev]

Upon inspecting the axe-core codebase with the help of Claude Code, it seems that all violations should have non-null impacts. Null impacts are reserved for passing checks. So internally, we'll assume that impact is always non-null, and throw an error if we encounter a null impact from Axe.