Keep term definitions mapping to null so they may be protected.

Author: gkellogg

CHANGELOG.md

@@ -19,6 +19,9 @@
 - Terms of the form of an IRI must map to the same IRI.
 - Terms of the form of a relative IRI may not be used as prefixes.
 
+### Changed
+- Keep term definitions mapping to null so they may be protected.
+
 ## 2.0.0 - 2019-12-09
 
 ### Notes

lib/context.js

@@ -365,16 +365,9 @@ api.createTermDefinition = ({
     activeCtx.mappings.delete(term);
   }
 
-  // clear context entry
-  if(value === null || (_isObject(value) && value['@id'] === null)) {
-    activeCtx.mappings.set(term, null);
-    defined.set(term, true);
-    return;
-  }
-
   // convert short-hand value to object w/@id
   let simpleTerm = false;
-  if(_isString(value)) {
+  if(_isString(value) || value === null) {
     simpleTerm = true;
     value = {'@id': value};
   }
@@ -448,13 +441,16 @@ api.createTermDefinition = ({
     mapping.reverse = true;
   } else if('@id' in value) {
     let id = value['@id'];
-    if(!_isString(id)) {
+    if(id && !_isString(id)) {
       throw new JsonLdError(
         'Invalid JSON-LD syntax; a @context @id value must be an array ' +
         'of strings or a string.',
         'jsonld.SyntaxError', {code: 'invalid IRI mapping', context: localCtx});
     }
-    if(id !== term) {
+    if(id === null) {
+      // reserve a null term, which may be protected
+      mapping['@id'] = null;
+    } else if(id !== term) {
       // expand and add @id mapping
       id = _expandIri(
         activeCtx, id, {vocab: true, base: false}, localCtx, defined, options);
@@ -470,10 +466,12 @@ api.createTermDefinition = ({
       if(term.match(/(?::[^:])|\//)) {
         const termDefined = new Map(defined).set(term, true);
         const termIri = _expandIri(
-          activeCtx, term, {vocab: true, base: false}, localCtx, termDefined, options);
+          activeCtx, term, {vocab: true, base: false},
+          localCtx, termDefined, options);
         if(termIri !== id) {
           throw new JsonLdError(
-            'Invalid JSON-LD syntax; term in form of IRI must expand to definition.',
+            'Invalid JSON-LD syntax; term in form of IRI must ' +
+            'expand to definition.',
             'jsonld.SyntaxError',
             {code: 'invalid IRI mapping', context: localCtx});
         }
@@ -942,6 +940,9 @@ api.getInitialContext = options => {
       let container = mapping['@container'] || '@none';
       container = [].concat(container).sort().join('');
 
+      if(mapping['@id'] === null) {
+        continue;
+      }
       // iterate over every IRI in the mapping
       const ids = _asArray(mapping['@id']);
       for(const iri of ids) {

tests/test-common.js

@@ -100,8 +100,6 @@ const TEST_TYPES = {
         /expand-manifest.jsonld#thc03$/,
         /expand-manifest.jsonld#thc04$/,
         /expand-manifest.jsonld#thc05$/,
-        // protected null IRI mapping
-        /expand-manifest.jsonld#tpr28$/,
         // remote
         /remote-doc-manifest.jsonld#t0005$/,
         /remote-doc-manifest.jsonld#t0006$/,
@@ -376,8 +374,6 @@ const TEST_TYPES = {
         /toRdf-manifest.jsonld#tpi09$/,
         /toRdf-manifest.jsonld#tpi10$/,
         /toRdf-manifest.jsonld#tpi11$/,
-        // protected null IRI mapping
-        /toRdf-manifest.jsonld#tpr28$/,
         // prefix
         /toRdf-manifest.jsonld#tpr29$/,
         // @import