diff --git a/js/codemeta_generation.js b/js/codemeta_generation.js
index 1275d8f..e072f07 100644
--- a/js/codemeta_generation.js
+++ b/js/codemeta_generation.js
@@ -1,284 +1,281 @@
 /**
  * Copyright (C) 2019-2020  The Software Heritage developers
  * See the AUTHORS file at the top-level directory of this distribution
  * License: GNU Affero General Public License version 3, or any later version
  * See top-level LICENSE file for more information
  */
 
 "use strict";
 
 const CODEMETA_CONTEXT_URL = 'https://doi.org/10.5063/schema/codemeta-2.0';
 const CONTEXTS = {
     [CODEMETA_CONTEXT_URL]: `${window.location.origin}/contexts/codemeta.jsonld`
 }
 
 const SPDX_PREFIX = 'https://spdx.org/licenses/';
 
 const jsonldCustomLoader = url => {
     const xhrDocumentLoader = jsonld.documentLoaders.xhr();
     if (url in CONTEXTS) {
         return xhrDocumentLoader(CONTEXTS[url]);
     }
     return xhrDocumentLoader(url);
 };
 
 function emptyToUndefined(v) {
     if (v == null || v == "")
         return undefined;
     else
         return v;
 }
 
 function getIfSet(query) {
     return emptyToUndefined(document.querySelector(query).value);
 }
 
 function setIfDefined(query, value) {
     if (value !== undefined) {
         document.querySelector(query).value = value;
     }
 }
 
 function getLicenses() {
     let selectedLicenses = Array.from(document.getElementById("selected-licenses").children);
     return selectedLicenses.map(licenseDiv => SPDX_PREFIX + licenseDiv.children[0].innerText);
 }
 
 // Names of codemeta properties with a matching HTML field name
 const directCodemetaFields = [
     'codeRepository',
     'contIntegration',
     'dateCreated',
     'datePublished',
     'dateModified',
     'downloadUrl',
     'issueTracker',
     'name',
     'version',
     'identifier',
     'description',
     'applicationCategory',
     'releaseNotes',
     'funding',
     'developmentStatus',
     'isPartOf',
     'referencePublication'
 ];
 
 const splittedCodemetaFields = [
     ['keywords', ','],
     ['programmingLanguage', ','],
     ['runtimePlatform', ','],
     ['operatingSystem', ','],
     ['softwareRequirements', '\n'],
     ['relatedLink', '\n'],
 ]
 
 // Names of codemeta properties with a matching HTML field name,
 // in a Person object
 const directPersonCodemetaFields = [
     'givenName',
     'familyName',
     'email',
     'affiliation',
 ];
 
 function generateShortOrg(fieldName) {
     var affiliation = getIfSet(fieldName);
     if (affiliation !== undefined) {
         if (isUrl(affiliation)) {
             return {
                 "@type": "Organization",
                 "@id": affiliation,
             };
         }
         else {
             return {
                 "@type": "Organization",
                 "name": affiliation,
             };
         }
     }
     else {
         return undefined;
     }
 }
 
 function generatePerson(idPrefix) {
     var doc = {
         "@type": "Person",
-        "@id": getIfSet(`#${idPrefix}_id`),
+    }
+    var id = getIfSet(`#${idPrefix}_id`);
+    if (id !== undefined) {
+        doc["@id"] = id;
     }
     directPersonCodemetaFields.forEach(function (item, index) {
         doc[item] = getIfSet(`#${idPrefix}_${item}`);
     });
     doc["affiliation"] = generateShortOrg(`#${idPrefix}_affiliation`)
 
     return doc;
 }
 
 function generatePersons(prefix) {
     var persons = [];
     var nbPersons = getNbPersons(prefix);
 
     for (let personId = 1; personId <= nbPersons; personId++) {
         persons.push(generatePerson(`${prefix}_${personId}`));
     }
 
     return persons;
 }
 
 
 function buildDoc() {
     var doc = {
         "@context": CODEMETA_CONTEXT_URL,
         "@type": "SoftwareSourceCode",
     };
 
     let licenses = getLicenses();
     if (licenses.length > 0) {
         doc["license"] = licenses;
     }
 
     // Generate most fields
     directCodemetaFields.forEach(function (item, index) {
         doc[item] = getIfSet('#' + item)
     });
 
     doc["funder"] = generateShortOrg('#funder', doc["affiliation"]);
 
     // Generate simple fields parsed simply by splitting
     splittedCodemetaFields.forEach(function (item, index) {
         const id = item[0];
         const separator = item[1];
         const value = getIfSet('#' + id);
         if (value !== undefined) {
             doc[id] = value.split(separator).map(trimSpaces);
         }
     });
 
     // Generate dynamic fields
     var authors = generatePersons('author');
     if (authors.length > 0) {
         doc["author"] = authors;
     }
     var contributors = generatePersons('contributor');
     if (contributors.length > 0) {
         doc["contributor"] = contributors;
     }
     return doc;
 }
 
-// FIXME this hack to make expansion work for now
-// (expansion does not accept empty values)
-function deleteEmptyValues(doc) {
-  return JSON.parse(JSON.stringify(doc));
-}
-
 async function generateCodemeta() {
     var inputForm = document.querySelector('#inputForm');
     var codemetaText, errorHTML;
 
     if (inputForm.checkValidity()) {
         var doc = buildDoc();
-        const expanded = await jsonld.expand(deleteEmptyValues(doc), {documentLoader: jsonldCustomLoader});
+        const expanded = await jsonld.expand(doc, {documentLoader: jsonldCustomLoader});
         const compacted = await jsonld.compact(expanded, CODEMETA_CONTEXT_URL, {documentLoader: jsonldCustomLoader});
         codemetaText = JSON.stringify(compacted, null, 4);
         errorHTML = "";
     }
     else {
         codemetaText = "";
         errorHTML = "invalid input (see error above)";
         inputForm.reportValidity();
     }
 
     document.querySelector('#codemetaText').innerText = codemetaText;
     setError(errorHTML);
 
 
     // Run validator on the exported value, for extra validation.
     // If this finds a validation, it means there is a bug in our code (either
     // generation or validation), and the generation MUST NOT generate an
     // invalid codemeta file, regardless of user input.
     if (codemetaText && !validateDocument(JSON.parse(codemetaText))) {
         alert('Bug detected! The data you wrote is correct; but for some reason, it seems we generated an invalid codemeta.json. Please report this bug at https://github.com/codemeta/codemeta-generator/issues/new and copy-paste the generated codemeta.json file. Thanks!');
     }
 
     if (codemetaText) {
         // For restoring the form state on page reload
         sessionStorage.setItem('codemetaText', codemetaText);
     }
 }
 
 // Imports a single field (name or @id) from an Organization.
 function importShortOrg(fieldName, doc) {
     if (doc !== undefined) {
         // Use @id if set, else use name
         setIfDefined(fieldName, doc["name"]);
         setIfDefined(fieldName, doc["@id"]);
     }
 }
 
 function importPersons(prefix, legend, docs) {
     if (docs === undefined) {
         return;
     }
 
     docs.forEach(function (doc, index) {
         var personId = addPerson(prefix, legend);
 
         setIfDefined(`#${prefix}_${personId}_id`, doc['@id']);
         directPersonCodemetaFields.forEach(function (item, index) {
             setIfDefined(`#${prefix}_${personId}_${item}`, doc[item]);
         });
 
         importShortOrg(`#${prefix}_${personId}_affiliation`, doc['affiliation'])
     })
 }
 
 function importCodemeta() {
     var inputForm = document.querySelector('#inputForm');
     var doc = parseAndValidateCodemeta(false);
     resetForm();
 
     if (doc['license'] !== undefined) {
         if (typeof doc['license'] === 'string') {
             doc['license'] = [doc['license']];
         }
 
         doc['license'].forEach(l => {
             if (l.indexOf(SPDX_PREFIX) !== 0) { return; }
             let licenseId = l.substring(SPDX_PREFIX.length);
             insertLicenseElement(licenseId);
         });
     }
 
     directCodemetaFields.forEach(function (item, index) {
         setIfDefined('#' + item, doc[item]);
     });
     importShortOrg('#funder', doc["funder"]);
 
     // Import simple fields by joining on their separator
     splittedCodemetaFields.forEach(function (item, index) {
         const id = item[0];
         const separator = item[1];
         let value = doc[id];
         if (value !== undefined) {
             if (Array.isArray(value)) {
                 value = value.join(separator);
             }
             setIfDefined('#' + id, value);
         }
     });
 
     importPersons('author', 'Author', doc['author'])
     importPersons('contributor', 'Contributor', doc['contributor'])
 }
 
 function loadStateFromStorage() {
     var codemetaText = sessionStorage.getItem('codemetaText')
     if (codemetaText) {
         document.querySelector('#codemetaText').innerText = codemetaText;
         importCodemeta();
     }
 }