Should not be necessary to copy TemplateResult

[Sofie-Bergqvist]

• lit-element: v2.5.1

We are having some trouble with the TemplateResult rendering, it should not be necessary to copy the TemplateResult Object and return a new TemplateResult to get the proper output.

This method seems to make the TemplateResult render fine.

private copyTemplateResult(data: TemplateResult): TemplateResult {
        let { strings, values, type, processor } = data;
        return new TemplateResult(strings, values, type, processor);
    }

However this method returns [Object] [Object]

private copyTemplateResult(data: TemplateResult): TemplateResult {
        return data;
    }

Here is one example of what we have tested: This method renders fine

private func(): TemplateResult {
        return this.getTemplateResultFromProperty;
    }

However, this method does not work. We think the output of these two should not differ.

    private func2(): TemplateResult {
        return html`${this.getTemplateResultFromProperty}´;
    }

The above method (func2) returns an error:
Uncaught (in promise) TypeError: Cannot read property 'split' of null at new Template (template.js:87)