Investigation: html${nothing} pattern is required for type safety with decorators

[Copilot]

Investigated whether html${nothing}`` should be replaced with direct nothing returns in Lit components. Answer: No - the wrapper is required for type safety.

Root Cause

Decorators @errorGuard() and @bindingGuard() enforce return type GenericRender<T> = TemplateResult<T>. Direct nothing returns fail because nothing is symbol, not TemplateResult<T>.

// ❌ Breaks with decorators
@errorGuard()
render() {
  return nothing;  // Type error: symbol not assignable to TemplateResult<T>
}

// ✅ Required pattern
@errorGuard()
render() {
  return html`${nothing}`;  // Creates TemplateResult<T> wrapping the symbol
}

Investigation Summary

• 21 occurrences tested across 20 files
• TypeScript compilation failed with decorator type errors
• Alternative type definitions broke all decorator-using components
• Changes reverted - current pattern is correct

Documentation

Added INVESTIGATION-NOTHING-PATTERN.md with detailed analysis including:

• Type system constraints
• Compilation errors encountered
• Pattern usage matrix
• Alternative approaches attempted

No code changes required. Current implementation is type-safe and correct.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[DXUI]: Return nothing instead of html`${nothing}`</issue_title>
<issue_description>### Task Description

Should we return nothing instead of html`${nothing}`?
Study the question and implement.

Acceptance Criteria

• Should remain typesafe & build
• Should pass existing tests

Technical Notes

No response

Jira Ticket

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [DXUI]: Return nothing instead of ` html${nothing} ` #6568

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