fix: prevent number format exception for number learning events

pom-dependency-tree.txt

@@ -1,4 +1,4 @@
-ai.elimu:webapp:war:2.6.103-SNAPSHOT
+ai.elimu:webapp:war:2.6.105-SNAPSHOT
 +- ai.elimu:model:jar:model-2.0.114:compile
 |  \- com.google.code.gson:gson:jar:2.13.1:compile
 |     \- com.google.errorprone:error_prone_annotations:jar:2.38.0:compile

src/main/java/ai/elimu/util/csv/CsvAnalyticsExtractionHelper.java

@@ -338,11 +338,15 @@ public static List<NumberLearningEvent> extractNumberLearningEvents(File csvFile
                 Integer numberValue = Integer.valueOf(csvRecord.get("number_value"));
                 numberLearningEvent.setNumberValue(numberValue);
 
-                String numberSymbol = csvRecord.get("number_symbol");
-                numberLearningEvent.setNumberSymbol(numberSymbol);
+                if (StringUtils.isNotBlank(csvRecord.get("number_symbol"))) {
+                    String numberSymbol = csvRecord.get("number_symbol");
+                    numberLearningEvent.setNumberSymbol(numberSymbol);
+                }
 
-                Long numberId = Long.valueOf(csvRecord.get("number_id"));
-                numberLearningEvent.setNumberId(numberId);
+                if (StringUtils.isNotBlank(csvRecord.get("number_id"))) {
+                    Long numberId = Long.valueOf(csvRecord.get("number_id"));
+                    numberLearningEvent.setNumberId(numberId);
+                }
 
                 numberLearningEvents.add(numberLearningEvent);
             }

src/test/java/ai/elimu/util/csv/CsvAnalyticsExtractionHelperTest.java

@@ -17,6 +17,7 @@
 
 import ai.elimu.entity.analytics.LetterSoundLearningEvent;
 import ai.elimu.entity.analytics.NumberAssessmentEvent;
+import ai.elimu.entity.analytics.NumberLearningEvent;
 import ai.elimu.entity.analytics.StoryBookLearningEvent;
 import ai.elimu.entity.analytics.VideoLearningEvent;
 import ai.elimu.entity.analytics.WordAssessmentEvent;
@@ -189,6 +190,30 @@ public void testExtractWordLearningEvents_v3005009() throws IOException {
     }
 
 
+    /**
+     * Test extraction of data from CSV files generated by version 4000028 of the Analytics app: 
+     * https://github.com/elimu-ai/analytics/releases/tag/4.0.28
+     */
+    @Test
+    public void testExtractNumberLearningEvents_v4000028() throws IOException {
+        ResourceLoader resourceLoader = new ClassRelativeResourceLoader(CsvAnalyticsExtractionHelper.class);
+        Resource resource = resourceLoader.getResource("5b7c682a12ecbe2e_4000028_number-learning-events_2025-07-04.csv");
+        File csvFile = resource.getFile();
+
+        List<NumberLearningEvent> numberLearningEvents = CsvAnalyticsExtractionHelper.extractNumberLearningEvents(csvFile);
+        assertEquals(1, numberLearningEvents.size());
+
+        NumberLearningEvent numberLearningEvent = numberLearningEvents.get(0);
+        assertEquals(1751610361 * 1_000L, numberLearningEvent.getTimestamp().getTimeInMillis());
+        assertEquals("5b7c682a12ecbe2e", numberLearningEvent.getAndroidId());
+        assertEquals("ai.elimu.calculator.debug", numberLearningEvent.getPackageName());
+        assertEquals(numberLearningEvent.getResearchExperiment(), ResearchExperiment.EXP_0_WORD_EMOJIS);
+        assertEquals(numberLearningEvent.getExperimentGroup(), ExperimentGroup.TREATMENT);
+        assertEquals(5, numberLearningEvent.getNumberValue());
+        assertNull(numberLearningEvent.getNumberSymbol());
+        assertNull(numberLearningEvent.getNumberId());
+    }
+
     /**
      * Test extraction of data from CSV files generated by version 4000028 of the Analytics app: 
      * https://github.com/elimu-ai/analytics/releases/tag/4.0.28

src/test/resources/ai/elimu/util/csv/5b7c682a12ecbe2e_4000028_number-learning-events_2025-07-04.csv

@@ -0,0 +1,2 @@
+id,timestamp,package_name,additional_data,learning_event_type,research_experiment,experiment_group,number_value,number_symbol,number_id
+46,1751610361,ai.elimu.calculator.debug,,,0,1,5,,