Return collections not None

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.