title: What is the $condition input parameter for in a GraphQL mutation generated by AWS Amplify CLI?
body: <p>I have generated a simple GraphQL API on AWS AppSync (using CLI) from this model:</p>
  <pre><code>type WalletProperty @model {
      id: ID!
      title: String!
  }
  </code></pre>
  <p>This generated a CreateWalletProperty, UpdateWalletProperty and DeleteWalletProperty mutations all similar to this:</p>
  <pre><code>  mutation CreateWalletProperty(
      $input: CreateWalletPropertyInput!
      $condition: ModelWalletPropertyConditionInput    &lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;  what is this for?
    ) {
      createWalletProperty(input: $input, condition: $condition) {
        id
        title
        createdAt
        updatedAt
      }
    }
  </code></pre>
  <p>and the schema for the condition being:</p>
  <pre><code>input ModelWalletPropertyConditionInput {
    title: ModelStringInput
    and: [ModelWalletPropertyConditionInput]
    or: [ModelWalletPropertyConditionInput]
    not: ModelWalletPropertyConditionInput
  }
  </code></pre>
  <p>Given that I always have to supply the mandatory $input, what is the $condition parameter for?</p>