code: function ensureConstructor (path: NodePath) {
    let lastProperty;
    const [existing] = path.get('body.body').filter(
      item => {
        if (item.isClassProperty()) {
          lastProperty = item;
          return false;
        }
        return item.node.kind === 'constructor';
      }
    );
    if (existing) {
      return existing;
    }
    let constructorNode;
    if (path.has('superClass')) {
      const args = t.identifier('args');
      constructorNode = t.classMethod(
        'constructor',
        t.identifier('constructor'),
        [t.restElement(args)],
        t.blockStatement([
          t.expressionStatement(
            t.callExpression(
              t.super(),
              [t.spreadElement(args)]
            )
          )
        ])
      );
  
    }
    else {
      constructorNode = t.classMethod(
        'constructor',
        t.identifier('constructor'),
        [],
        t.blockStatement([])
      );
    }
  
    if (lastProperty) {
      lastProperty.insertAfter(constructorNode);
    }
    else {
      path.get('body').unshiftContainer('body', constructorNode);
    }
  }
docs: Ensure that the given class contains a constructor.