anthropic.ContentBlockSourceContentUnionParam does not seem to marshal correctly

[paddyjok]

When trying to use the SDK to add a Custom Content Document eg:

{
    "type": "document",
    "source": {
        "type": "content",
        "content": [
            {"type": "text", "text": "The grass is green."},
            {"type": "text", "text": "The sky is blue."}
        ]
    },
    "title": "Document Title", # optional
    "context": "Context about the document that will not be cited from", # optional
    "citations": {"enabled": True}
}

using this code:

        // Create content blocks for the structured document
	contentBlocks := []anthropic.ContentBlockSourceContentUnionParam{
		{
			OfString: param.NewOpt("The grass is green."),
		},
		{
			OfString: param.NewOpt("The sky is blue."),
		},
	}

	// Create the document with content source (structured content for citations)
	documentBlock := anthropic.NewDocumentBlock(anthropic.ContentBlockSourceParam{
		Content: anthropic.ContentBlockSourceContentUnionParam{
			OfContentBlockSourceContent: contentBlocks,
		},
	})

I get the following error from the API:

{"type":"error","error":{"type":"invalid_request_error","message":"messages.0.content.0.document.source.content.content.0: Input should be a valid dictionary or object to extract fields from"},"request_id":"req_011CSoQmM3LxgiryWij2SwUt"}

Looking at the json that was marshaled, we get:

 {
	                   "source": {
	                        "content": [
	                            "The grass is green.",  <----- these should be objects with type and text keys  {"type": "text", "text": "The grass is green."}
	                            "The sky is blue."
	                         ],
	                         "type": "content"
	                     },
	                     "context": "This is a trustworthy document.",
	                    "title": "My Document",
	                    "citations": {
	                         "enabled": true
	                     },
	                     "type": "document"
	                 },

It looks like the SDK is not marshaling these correctly.