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.
doc is the raw Document map containing type value.
defaultValue is the fallback value if type is not found.
Returns the extracted Document type (or defaultValue if not present).
Implementation
String? getDocumentType(Mapping doc, [String? defaultValue]);