fix: Handle empty datapoints in otel exporter (#1898)

From @dhoard on slack, There was an error in the jmx-exporter project
smoke tests:


> time=2026-02-16T15:49:03.466Z level=ERROR source=write_handler.go:652
msg="Error appending remote write" component=web err="empty data points.
jvm_memory_pool_allocated_bytes is dropped"
> 2026-02-16 15:49:03.482 | OkHttp http://prometheus:9090/... | WARNING
|
e1723a08afd7bca35570fd31a7656f59.io.prometheus.metrics.shaded.io_opentelemetry_2_25_0_alpha.exporter.internal.http.HttpExporter
| Failed to export metrics. Server responded with HTTP status code 500.
Error message: Unable to parse response body, HTTP status message:
Internal Server Error



> Looking at the documentation for `jvm_memory_pool_allocated_bytes`...
"Only updated after GC, not continuously." Most likely GC hasn't
happened, yet the OTel exporter is trying to write the data.

I updated the method to return null when the data points are empty,
which is then handled via the
[addUnlessNull](https://github.com/prometheus/client_java/blob/main/prometheus-metrics-exporter-opentelemetry/src/main/java/io/prometheus/metrics/exporter/opentelemetry/PrometheusMetricProducer.java#L136)
method.

After applying this change locally, I ran the [quick
test](https://github.com/prometheus/jmx_exporter/blob/main/run-quick-test.sh)
a few times and the error was no longer present.

---------

Signed-off-by: Jay DeLuca <jaydeluca4@gmail.com>

Author: jaydeluca

prometheus-metrics-exporter-opentelemetry/src/main/java/io/prometheus/metrics/exporter/opentelemetry/otelmodel/MetricDataFactory.java

@@ -27,15 +27,23 @@ public MetricDataFactory(
     this.currentTimeMillis = currentTimeMillis;
   }
 
+  @Nullable
   public MetricData create(CounterSnapshot snapshot) {
+    if (snapshot.getDataPoints().isEmpty()) {
+      return null;
+    }
     return new PrometheusMetricData<>(
         snapshot.getMetadata(),
         new PrometheusCounter(snapshot, currentTimeMillis),
         instrumentationScopeInfo,
         resource);
   }
 
+  @Nullable
   public MetricData create(GaugeSnapshot snapshot) {
+    if (snapshot.getDataPoints().isEmpty()) {
+      return null;
+    }
     return new PrometheusMetricData<>(
         snapshot.getMetadata(),
         new PrometheusGauge(snapshot, currentTimeMillis),
@@ -64,31 +72,47 @@ public MetricData create(HistogramSnapshot snapshot) {
     return null;
   }
 
+  @Nullable
   public MetricData create(SummarySnapshot snapshot) {
+    if (snapshot.getDataPoints().isEmpty()) {
+      return null;
+    }
     return new PrometheusMetricData<>(
         snapshot.getMetadata(),
         new PrometheusSummary(snapshot, currentTimeMillis),
         instrumentationScopeInfo,
         resource);
   }
 
+  @Nullable
   public MetricData create(InfoSnapshot snapshot) {
+    if (snapshot.getDataPoints().isEmpty()) {
+      return null;
+    }
     return new PrometheusMetricData<>(
         snapshot.getMetadata(),
         new PrometheusInfo(snapshot, currentTimeMillis),
         instrumentationScopeInfo,
         resource);
   }
 
+  @Nullable
   public MetricData create(StateSetSnapshot snapshot) {
+    if (snapshot.getDataPoints().isEmpty()) {
+      return null;
+    }
     return new PrometheusMetricData<>(
         snapshot.getMetadata(),
         new PrometheusStateSet(snapshot, currentTimeMillis),
         instrumentationScopeInfo,
         resource);
   }
 
+  @Nullable
   public MetricData create(UnknownSnapshot snapshot) {
+    if (snapshot.getDataPoints().isEmpty()) {
+      return null;
+    }
     return new PrometheusMetricData<>(
         snapshot.getMetadata(),
         new PrometheusUnknown(snapshot, currentTimeMillis),

prometheus-metrics-exporter-opentelemetry/src/test/java/io/prometheus/metrics/exporter/opentelemetry/ExportTest.java

@@ -33,7 +33,7 @@ class ExportTest {
 
   private static final Attributes ATTRIBUTES =
       Attributes.of(AttributeKey.stringKey("label"), "val", AttributeKey.stringKey("key"), "value");
-  @RegisterExtension OpenTelemetryExtension testing = OpenTelemetryExtension.create();
+  @RegisterExtension static OpenTelemetryExtension testing = OpenTelemetryExtension.create();
 
   private final PrometheusRegistry registry = new PrometheusRegistry();
 
@@ -304,6 +304,26 @@ void unknown() {
                             .hasAttributes(Attributes.of(AttributeKey.stringKey("label"), "val"))));
   }
 
+  @Test
+  void metricsWithoutDataPointsAreNotExported() {
+    // Register metrics with labels but don't create any data points
+    // This simulates the jvm_memory_pool_allocated_bytes scenario where a metric
+    // is registered with label names, but no data points are created until GC happens
+    Counter.builder().name("counter_no_data").labelNames("pool").register(registry);
+    Gauge.builder().name("gauge_no_data").labelNames("pool").register(registry);
+    Summary.builder().name("summary_no_data").labelNames("pool").register(registry);
+    Histogram.builder().name("histogram_no_data").labelNames("pool").register(registry);
+    StateSet.builder()
+        .name("stateset_no_data")
+        .states("state")
+        .labelNames("pool")
+        .register(registry);
+    Info.builder().name("info_no_data").labelNames("pool").register(registry);
+
+    List<MetricData> metrics = testing.getMetrics();
+    assertThat(metrics).isEmpty();
+  }
+
   private MetricAssert metricAssert() {
     List<MetricData> metrics = testing.getMetrics();
     assertThat(metrics).hasSize(1);