Also allow null directions

Author: rubensworks

data-model.d.ts

@@ -76,7 +76,7 @@ export interface Literal {
     /**
      * the direction of the language-tagged string.
      */
-    direction?: 'ltr' | 'rtl' | '';
+    direction?: 'ltr' | 'rtl' | '' | null;
     /**
      * A NamedNode whose IRI represents the datatype of the literal.
      */
@@ -298,5 +298,5 @@ export interface DataFactory<OutQuad extends BaseQuad = Quad, InQuad extends Bas
 
 export interface DirectionalLanguage {
     language: string;
-    direction?: 'ltr' | 'rtl' | '';
+    direction?: 'ltr' | 'rtl' | '' | null;
 }

rdf-js-tests.ts

@@ -36,7 +36,7 @@ function test_terms() {
     const termType3: string = literal.termType;
     const value3: string = literal.value;
     const language3: string = literal.language;
-    const dir3: 'ltr' | 'rtl' | '' | undefined = literal.direction;
+    const dir3: 'ltr' | 'rtl' | '' | null | undefined = literal.direction;
     const datatype3: NamedNode = literal.datatype;
     let literalEqual: boolean = literal.equals(someTerm);
     literalEqual = literal.equals(null);