v0.13.1

• Fixed. A JSON body property declaring OAS 3.0 nullable: true beside
  a bound yielded no body case for any category: JsonBodyWitness withheld
  its candidates from the check, on the reasoning that a schema admitting
  null promises nothing about what is written over it — but null is
  admitted in addition to the declared keywords, and a string longer than
  maxLength is no more valid for it. The candidates now go to
  WitnessCheck like every other property's, which already approved them.
  Under OAS 3.1 nothing changes: nullable is not a keyword there, the
  contract refuses the schema and the check fails closed — spell it as a
  type union containing null (#112).