Amplify-cli: amplify mock failed to start when using @key directives

[nujhong]

Describe the bug
Hi there, I am getting the following error when running amplify mock: Failed to start API Mock endpoint ValidationException: The number of attributes in key schema must match the number of attributesdefined in attribute definitions.

To Reproduce

schema.graphql type Customer @model @key(fields: ["id", "updatedAt"]) @key(name: "BySpending", fields: ["id", "totalSpending"]) @key(name: "ByAttendance", fields: ["id", "totalAttendance"]) @auth(rules: [{ allow: owner }, { allow: groups, groups: ["Admin"] }]) { id: ID! ... totalSpending: Int! totalAttendance: Int! ... entries: [Entry] @connection(name: "CustomerEntries") ... owner: ID! createdAt: AWSDateTime updatedAt: AWSDateTime! }

Expected behavior
Create two LSI and start AppSync Mock service.
The schema above should have met the LSI requirement:

Every local secondary index must meet the following conditions:

• The partition key is the same as that of its base table.
• The sort key consists of exactly one scalar attribute.
• The sort key of the base table is projected into the index, where it acts as a non-key attribute.

Screenshots
It seems OK when pushing to cloud

Desktop (please complete the following information):

• OS: macOS Mojave
• amplify-cli: 3.15
• node: 10.16.3

Additional context
related #1725 #2059

[tt-anh-eole]

Same error.

[rinosamakanata]

I can reproduce this error, too.