fix(form): fix isNew property for empty answers

addon/lib/answer.js

@@ -6,6 +6,7 @@ import { inject as service } from "@ember/service";
 import { decodeId } from "ember-caluma/helpers/decode-id";
 import { getOwner } from "@ember/application";
 import { parseDocument } from "ember-caluma/lib/parsers";
+import { isEmpty } from "@ember/utils";
 
 /**
  * Object which represents an answer in context of a field
@@ -40,6 +41,10 @@ export default Base.extend({
     return this.raw.id ? decodeId(this.raw.id) : null;
   }),
 
+  isNew: computed("uuid", "value", function() {
+    return !this.uuid || isEmpty(this.value);
+  }),
+
   /**
    * The name of the property in which the value is stored. This depends on the
    * type of the answer.

addon/lib/field.js

@@ -1,6 +1,6 @@
 import Base from "ember-caluma/lib/base";
 import { computed, getWithDefault, defineProperty } from "@ember/object";
-import { equal, not, reads, empty } from "@ember/object/computed";
+import { equal, not, reads } from "@ember/object/computed";
 import { inject as service } from "@ember/service";
 import { assert } from "@ember/debug";
 import { getOwner } from "@ember/application";
@@ -178,12 +178,14 @@ export default Base.extend({
   isInvalid: not("isValid"),
 
   /**
-   * Whether the field is new (never saved to the backend service)
+   * Whether the field is new (never saved to the backend service or empty)
    *
    * @property {Boolean} isNew
    * @accessor
    */
-  isNew: empty("answer.pk"),
+  isNew: computed("answer.isNew", function() {
+    return !this.answer || this.answer.isNew;
+  }),
 
   /**
    * The type of the question

tests/unit/lib/field-test.js

@@ -87,10 +87,20 @@ module("Unit | Library | field", function(hooks) {
   });
 
   test("computes isNew correctly", async function(assert) {
-    assert.expect(2);
+    assert.expect(3);
+
+    const answeredField = this.document.findField("test-question");
+    const unansweredField = this.document.findField("test-question-3");
+
+    assert.equal(answeredField.isNew, false);
+    assert.equal(unansweredField.isNew, true);
+
+    const oldValue = answeredField.value;
+    answeredField.set("answer.value", null); // empty value
+
+    assert.equal(answeredField.isNew, true);
 
-    assert.equal(this.document.findField("test-question").isNew, false);
-    assert.equal(this.document.findField("test-question-3").isNew, true);
+    answeredField.set("answer.value", oldValue); // reset value
   });
 
   test("can compute the question", async function(assert) {