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Return empty collections (lists, dicts, sets) instead of None when representing empty states. This reduces null checking boilerplate, prevents null reference errors, and makes code more predictable. When a function returns a collection type, an empty collection communicates “no items” more clearly than None and allows direct operations without defensive checks.

Example:

# Not recommended
def extract_tags(span):
    if not span.tags:
        return None  # Forces callers to check for None
    return [tag for tag in span.tags]

# Recommended
def extract_tags(span):
    if not span.tags:
        return []  # Callers can immediately iterate/operate on result
    return [tag for tag in span.tags]

# Usage is simpler and safer
tags = extract_tags(span)
for tag in tags:  # Works directly, no None check needed
    process_tag(tag)

This pattern:

• Eliminates common None-check boilerplate
• Prevents NullPointerException scenarios
• Makes interfaces more predictable
• Allows direct operations on return values
• Maintains semantic clarity between “no items” vs “invalid/error state”

For error conditions or invalid states, raise exceptions or use Optional types instead of returning None.