remove union with null for return type. eslint was saying unknown tru…

…mps all other type designations anyway so it was pointless.

src/dataTransformers/StringDataTransformer.ts

@@ -11,7 +11,7 @@ class StringDataTransformer implements DataTransformer {
 	/** Transform mv string to js string */
 	public transformFromDb(value: null): null;
 	public transformFromDb(value: unknown): string;
-	public transformFromDb(value: unknown): unknown | null {
+	public transformFromDb(value: unknown): unknown {
 		if (value == null) {
 			// if this property has an enumeration constraint and one of those constraints is empty string then return empty string;
 			// otherwise return null