Sounds like you want something like

# To replace any empty value (including undefined):
my @list = map { $_ || 'N/A' } @fields;

# or, to replace only undefined values, leaving empty ones as empty st
+rings:
my @list = map { defined $_ ? $_ : 'N/A' } @fields;
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Season @fields to taste (for example, @fields might be the result of another map, or a split).