diff --git a/codemeta_generation.js b/codemeta_generation.js
index 0018b62..40c6f25 100644
--- a/codemeta_generation.js
+++ b/codemeta_generation.js
@@ -1,204 +1,208 @@
 /**
  * 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 SPDX_PREFIX = 'https://spdx.org/licenses/';
 
 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;
     }
 }
 
 // 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 generatePerson(idPrefix) {
     var doc = {
         "@type": "Person",
         "@id": getIfSet(`#${idPrefix}_id`),
     }
     directPersonCodemetaFields.forEach(function (item, index) {
         doc[item] = getIfSet(`#${idPrefix}_${item}`);
     });
 
     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 generateCodemeta() {
     var inputForm = document.querySelector('#inputForm');
     var codemetaText, errorHTML;
 
     if (inputForm.checkValidity()) {
         var doc = {
             "@context": "https://doi.org/10.5063/schema/codemeta-2.0",
             "@type": "SoftwareSourceCode",
-            "license": SPDX_PREFIX + getIfSet('#license'),
         };
 
+        var license = getIfSet('#license')
+        if (license !== undefined) {
+            doc["license"] = SPDX_PREFIX + getIfSet('#license');
+        }
+
         // Generate most fields
         directCodemetaFields.forEach(function (item, index) {
             doc[item] = getIfSet('#' + item)
         });
 
         // 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
         doc = Object.assign(doc, {
             "author": generatePersons('author'),
             "contributor": generatePersons('contributor'),
         });
 
         codemetaText = JSON.stringify(doc, null, 4);
         errorHTML = "";
     }
     else {
         codemetaText = "";
         errorHTML = "invalid input (see error above)";
         inputForm.reportValidity();
     }
 
     document.querySelector('#codemetaText').innerText = codemetaText;
     setError(errorHTML);
 
     if (codemetaText) {
         // For restoring the form state on page reload
         sessionStorage.setItem('codemetaText', codemetaText);
     }
 }
 
 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]);
         });
     })
 }
 
 function importCodemeta() {
     var inputForm = document.querySelector('#inputForm');
     var codemetaText = document.querySelector('#codemetaText').innerText;
     var doc;
 
     try {
         doc = JSON.parse(codemetaText);
     }
     catch (e) {
         setError(`Could not read codemeta document because it is not valid JSON (${e})`);
         return;
     }
     resetForm();
 
     if (doc['license'] !== undefined && doc['license'].indexOf(SPDX_PREFIX) == 0) {
         var license = doc['license'].substring(SPDX_PREFIX.length);
         document.querySelector('#license').value = license;
     }
 
     directCodemetaFields.forEach(function (item, index) {
         setIfDefined('#' + item, doc[item]);
     });
 
     // 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'])
 
     setError("");
 }
 
 function loadStateFromStorage() {
     var codemetaText = sessionStorage.getItem('codemetaText')
     if (codemetaText) {
         document.querySelector('#codemetaText').innerText = codemetaText;
         importCodemeta();
     }
 }
diff --git a/cypress/integration/basics.js b/cypress/integration/basics.js
index b6cf0e6..8fdf7c3 100644
--- a/cypress/integration/basics.js
+++ b/cypress/integration/basics.js
@@ -1,62 +1,61 @@
 /**
  * Copyright (C) 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
  */
 
 /*
  * Tests the basic features of the application.
  */
 
 "use strict";
 
 describe('JSON Generation', function() {
     beforeEach(function() {
         /* Clear the session storage, as it is used to restore field data;
          * and we don't want a test to load data from the previous test. */
         cy.window().then((win) => {
             win.sessionStorage.clear()
         })
         cy.visit('./index.html');
     });
 
     it('works just from the software name', function() {
         cy.get('#name').type('My Test Software');
         cy.get('#generateCodemeta').click();
 
         cy.get('#errorMessage').should('have.text', '');
         cy.get('#codemetaText').then((elem) => JSON.parse(elem.text()))
             .should('deep.equal', {
                 "@context": "https://doi.org/10.5063/schema/codemeta-2.0",
                 "@type": "SoftwareSourceCode",
-                "license": "https://spdx.org/licenses/undefined",
                 "name": "My Test Software",
                 "author": [],
                 "contributor": []
         });
     });
 
     it('works just from all main fields', function() {
         cy.get('#name').type('My Test Software');
         cy.get('#description').type('This is a\ngreat piece of software');
         cy.get('#dateCreated').type('2019-10-02');
         cy.get('#datePublished').type('2020-01-01');
         cy.get('#license').clear().type('AGPL-3.0');
         cy.get('#generateCodemeta').click();
 
         cy.get('#errorMessage').should('have.text', '');
         cy.get('#codemetaText').then((elem) => JSON.parse(elem.text()))
             .should('deep.equal', {
                 "@context": "https://doi.org/10.5063/schema/codemeta-2.0",
                 "@type": "SoftwareSourceCode",
                 "license": "https://spdx.org/licenses/AGPL-3.0",
                 "dateCreated": "2019-10-02",
                 "datePublished": "2020-01-01",
                 "name": "My Test Software",
                 "description": "This is a\ngreat piece of software",
                 "author": [],
                 "contributor": []
         });
     });
 });