Make sure that 0 cer and wer are reported

qurator/dinglehopper/templates/report.html.j2

@@ -40,13 +40,13 @@
 
 {% if metrics %}
 <h2>Metrics</h2>
-    {% if cer %}
+    {% if cer is not none %}
     <p>CER: {{ cer|round(4) }}</p>
     {% endif %}
-    {% if wer %}
+    {% if wer is not none %}
     <p>WER: {{ wer|round(4) }}</p>
     {% endif %}
-    {% if fca %}
+    {% if fca is not none %}
     <p>FCA: {{ fca|round(4) }}</p>
     {% endif %}
 {% endif %}

qurator/dinglehopper/templates/report.json.j2

@@ -1,10 +1,10 @@
 {
 {% if metrics %}
-    {% if cer %}"cer": {{ cer|json_float }},{% endif %}
-    {% if wer %}"wer": {{ wer|json_float }},{% endif %}
-    {% if fca %}"fca": {{ fca|json_float }},{% endif %}
-    {% if n_characters %}"n_characters": {{ n_characters }},{% endif %}
-    {% if n_words %}"n_words": {{ n_words }},{% endif %}
+    {% if cer is not none %}"cer": {{ cer|json_float }},{% endif %}
+    {% if wer is not none %}"wer": {{ wer|json_float }},{% endif %}
+    {% if fca is not none %}"fca": {{ fca|json_float }},{% endif %}
+    {% if n_characters is not none %}"n_characters": {{ n_characters }},{% endif %}
+    {% if n_words is not none %}"n_words": {{ n_words }},{% endif %}
 {% endif %}
     "gt": "{{ gt }}",
     "ocr": "{{ ocr }}"

qurator/dinglehopper/tests/test_integ_cli_valid_json.py

@@ -58,3 +58,18 @@ def test_cli_json_cer_is_infinity(tmp_path):
             j = json.load(jsonf)
             assert j["cer"] == pytest.approx(float("inf"))
             assert j["fca"] == pytest.approx(-13)
+
+
+def test_cli_json_cer_0_in_report(tmp_path):
+    """Test that the cli/process() yields a loadable JSON report when CER == 0"""
+
+    with working_directory(str(tmp_path)):
+        with open("gt.txt", "w") as gtf:
+            gtf.write("Lorem Ipsum")
+
+        process("gt.txt", "gt.txt", "report", metrics="cer,wer,fca")
+        with open("report.json", "r") as jsonf:
+            j = json.load(jsonf)
+            assert j["cer"] == pytest.approx(0)
+            assert j["wer"] == pytest.approx(0)
+            assert j["fca"] == pytest.approx(1)