getDocumentType abstract method
Extracts the document type from a raw Document map.
Retrieves the type identifier (e.g., "visa", "bulletin") from a raw Document map with a fallback default value if the type field is missing.
@param doc - Raw Document map containing type metadata
@param defaultValue - Fallback value if type is not found
@return Extracted Document type (or defaultValue if not present)
Implementation
String? getDocumentType(Mapping doc, [String? defaultValue]);