creator and author syntax question

Hi schema.org,

I am working on JSON-LD content for 'Dataset' type. The dataset has 
multiple authors. I used Google Rich Results Test Tool. 
https://search.google.com/test/rich-results?utm_campaign=sdtt&utm_medium=message

The following 'author' syntax is correct according the test tool. But if 
I replaced 'author' with 'creator', the tool said 'Invalid object type 
for field "creator". I read through schema.org documents, it seems both 
should work. Can someone explain why it failed on 'creator'?

"author": [
{
"@type": "Role", "roleName": "Lead Author",
"author": [
{
"@type": "Person",
"name": "C E Nehru",
"givenName": "C",
"familyName": "Nehru"
}
]
},
{
"@type": "Role", "roleName": "Coauthor",
"author": [
{
"@type": "Person",
"name": "Martin Prinz",
"givenName": "Martin",
"familyName": "Prinz"
},
{
"@type": "Person",
"name": "Eric Dowty",
"givenName": "Eric",
"familyName": "Dowty"
},
{
"@type": "Person",
"name": "Klaus Keil",
"givenName": "Klaus",
"familyName": "Keil"
}
]
}
],

Thanks,

Lulin Song
Geoinformatics
Lamont-Doherty Earth Observatory
Columbia University