docs: private boolean isUnresolvableTypeVariable() {
          if (this.type instanceof TypeVariable) {
              if (this.variableResolver == null) {
                  return true;
              }
              TypeVariable<?> variable = (TypeVariable<?>) this.type;
              ResolvableType resolved = this.variableResolver.resolveVariable(variable);
              if (resolved == null || resolved.isUnresolvableTypeVariable()) {
                  return true;
              }
          }
          return false;
      }