Package pgnull builds nullable pgx column values from plain Go values,
collapsing the empty value to SQL NULL. It replaces the per-package
`pgtype.Text{String: v, Valid: v != ""}` one-liners that accumulated across
the codebase so every call site shares one NULL convention.
Text returns a pgtype.Text that is NULL when s is empty and the string
otherwise. Use it for optional text columns where "" and NULL are the same
absence (the common case: optional foreign keys, optional metadata).
TextTrim is Text after trimming surrounding whitespace, so a value that is
blank once trimmed also becomes NULL. Use it at ingestion boundaries where
callers may pass whitespace-only strings.