--- a/toolkit/components/glean/api/src/ffi/macros.rs
+++ b/toolkit/components/glean/api/src/ffi/macros.rs
@@ -26,30 +26,36 @@ macro_rules! metric_get {
 ///
 /// * `$map`     - The name of the hash map within `metrics::__glean_metric_maps`
 ///                as generated by glean_parser.
 /// * `$id`      - The ID of the metric to get.
 /// * `$storage` - the storage name to look into.
 macro_rules! test_has {
     ($map:ident, $id:ident, $storage:ident) => {{
         let metric = metric_get!($map, $id);
-        let storage = $storage.to_utf8();
-        let storage = Some(&storage[..]);
-        metric.test_get_value(storage).is_some()
+        let storage = if $storage.is_empty() {
+            None
+        } else {
+            Some($storage.to_utf8())
+        };
+        metric.test_get_value(storage.as_deref()).is_some()
     }};
 }
 
 /// Get the currently stored value for the metric identified by its ID.
 ///
 /// # Arguments
 ///
 /// * `$map`     - The name of the hash map within `metrics::__glean_metric_maps`
 ///                as generated by glean_parser.
 /// * `$id`      - The ID of the metric to get.
 /// * `$storage` - the storage name to look into.
 macro_rules! test_get {
     ($map:ident, $id:ident, $storage:ident) => {{
         let metric = metric_get!($map, $id);
-        let storage = $storage.to_utf8();
-        let storage = Some(&storage[..]);
-        metric.test_get_value(storage).unwrap()
+        let storage = if $storage.is_empty() {
+            None
+        } else {
+            Some($storage.to_utf8())
+        };
+        metric.test_get_value(storage.as_deref()).unwrap()
     }};
 }

--- a/toolkit/components/glean/bindings/private/Boolean.h
+++ b/toolkit/components/glean/bindings/private/Boolean.h
@@ -33,23 +33,26 @@ class BooleanMetric {
    *
    * This function will attempt to await the last parent-process task (if any)
    * writing to the the metric's storage engine before returning a value.
    * This function will not wait for data from child processes.
    *
    * This doesn't clear the stored value.
    * Parent process only. Panics in child processes.
    *
+   * @param aPingName The (optional) name of the ping to retrieve the metric
+   *        for. Defaults to the first value in `send_in_pings`.
+   *
    * @return value of the stored metric.
    */
-  Maybe<bool> TestGetValue(const nsACString& aStorageName) const {
-    if (!fog_boolean_test_has_value(mId, &aStorageName)) {
+  Maybe<bool> TestGetValue(const nsACString& aPingName = nsCString()) const {
+    if (!fog_boolean_test_has_value(mId, &aPingName)) {
       return Nothing();
     }
-    return Some(fog_boolean_test_get_value(mId, &aStorageName));
+    return Some(fog_boolean_test_get_value(mId, &aPingName));
   }
 
  private:
   const uint32_t mId;
 };
 }  // namespace impl
 
 class GleanBoolean final : public nsIGleanBoolean {

--- a/toolkit/components/glean/bindings/private/Counter.h
+++ b/toolkit/components/glean/bindings/private/Counter.h
@@ -33,23 +33,26 @@ class CounterMetric {
    *
    * This function will attempt to await the last parent-process task (if any)
    * writing to the the metric's storage engine before returning a value.
    * This function will not wait for data from child processes.
    *
    * This doesn't clear the stored value.
    * Parent process only. Panics in child processes.
    *
+   * @param aPingName The (optional) name of the ping to retrieve the metric
+   *        for. Defaults to the first value in `send_in_pings`.
+   *
    * @return value of the stored metric, or Nothing() if there is no value.
    */
-  Maybe<int32_t> TestGetValue(const nsACString& aStorageName) const {
-    if (!fog_counter_test_has_value(mId, &aStorageName)) {
+  Maybe<int32_t> TestGetValue(const nsACString& aPingName = nsCString()) const {
+    if (!fog_counter_test_has_value(mId, &aPingName)) {
       return Nothing();
     }
-    return Some(fog_counter_test_get_value(mId, &aStorageName));
+    return Some(fog_counter_test_get_value(mId, &aPingName));
   }
 
  private:
   const uint32_t mId;
 };
 }  // namespace impl
 
 class GleanCounter final : public nsIGleanCounter {

--- a/toolkit/components/glean/bindings/private/Datetime.h
+++ b/toolkit/components/glean/bindings/private/Datetime.h
@@ -48,24 +48,28 @@ class DatetimeMetric {
    *
    * This function will attempt to await the last parent-process task (if any)
    * writing to the the metric's storage engine before returning a value.
    * This function will not wait for data from child processes.
    *
    * This doesn't clear the stored value.
    * Parent process only. Panics in child processes.
    *
+   * @param aPingName The (optional) name of the ping to retrieve the metric
+   *        for. Defaults to the first value in `send_in_pings`.
+   *
    * @return value of the stored metric, or Nothing() if there is no value.
    */
-  Maybe<nsCString> TestGetValue(const nsACString& aStorageName) const {
-    if (!fog_datetime_test_has_value(mId, &aStorageName)) {
+  Maybe<nsCString> TestGetValue(
+      const nsACString& aPingName = nsCString()) const {
+    if (!fog_datetime_test_has_value(mId, &aPingName)) {
       return Nothing();
     }
     nsCString ret;
-    fog_datetime_test_get_value(mId, &aStorageName, &ret);
+    fog_datetime_test_get_value(mId, &aPingName, &ret);
     return Some(ret);
   }
 
  private:
   const uint32_t mId;
 };
 }  // namespace impl
 

--- a/toolkit/components/glean/bindings/private/Event.h
+++ b/toolkit/components/glean/bindings/private/Event.h
@@ -68,21 +68,24 @@ class EventMetric {
    *
    * This function will attempt to await the last parent-process task (if any)
    * writing to the the metric's storage engine before returning a value.
    * This function will not wait for data from child processes.
    *
    * This doesn't clear the stored value.
    * Parent process only. Panics in child processes.
    *
+   * @param aPingName The (optional) name of the ping to retrieve the metric
+   *        for. Defaults to the first value in `send_in_pings`.
+   *
    * @return value of the stored metric, or Nothing() if there is no value.
    */
   Maybe<nsTArray<RecordedEvent>> TestGetValue(
-      const nsACString& aStorageName) const {
-    if (!fog_event_test_has_value(mId, &aStorageName)) {
+      const nsACString& aPingName = nsCString()) const {
+    if (!fog_event_test_has_value(mId, &aPingName)) {
       return Nothing();
     }
 
     // TODO(bug 1678567): Implement this.
     nsTArray<RecordedEvent> empty;
     return Some(std::move(empty));
   }
 

--- a/toolkit/components/glean/bindings/private/MemoryDistribution.h
+++ b/toolkit/components/glean/bindings/private/MemoryDistribution.h
@@ -46,19 +46,23 @@ class MemoryDistributionMetric {
    *
    * This function will attempt to await the last parent-process task (if any)
    * writing to the the metric's storage engine before returning a value.
    * This function will not wait for data from child processes.
    *
    * This doesn't clear the stored value.
    * Parent process only. Panics in child processes.
    *
+   * @param aPingName The (optional) name of the ping to retrieve the metric
+   *        for. Defaults to the first value in `send_in_pings`.
+   *
    * @return value of the stored metric, or Nothing() if there is no value.
    */
-  Maybe<DistributionData> TestGetValue(const nsACString& aPingName) const {
+  Maybe<DistributionData> TestGetValue(
+      const nsACString& aPingName = nsCString()) const {
     if (!fog_memory_distribution_test_has_value(mId, &aPingName)) {
       return Nothing();
     }
     nsTArray<uint64_t> buckets;
     nsTArray<uint64_t> counts;
     DistributionData ret;
     fog_memory_distribution_test_get_value(mId, &aPingName, &ret.sum, &buckets,
                                            &counts);

--- a/toolkit/components/glean/bindings/private/Ping.h
+++ b/toolkit/components/glean/bindings/private/Ping.h
@@ -35,17 +35,17 @@ class Ping {
    * Pings always contain the `ping_info` and `client_info` sections.
    * See [ping
    * sections](https://mozilla.github.io/glean/book/user/pings/index.html#ping-sections)
    * for details.
    *
    * @param aReason - Optional. The reason the ping is being submitted.
    *                  Must match one of the configured `reason_codes`.
    */
-  void Submit(const nsACString& aReason) const {
+  void Submit(const nsACString& aReason = nsCString()) const {
     fog_submit_ping_by_id(mId, &aReason);
   }
 
  private:
   const uint32_t mId;
 };
 
 }  // namespace impl

--- a/toolkit/components/glean/bindings/private/String.h
+++ b/toolkit/components/glean/bindings/private/String.h
@@ -37,24 +37,28 @@ class StringMetric {
    *
    * This function will attempt to await the last parent-process task (if any)
    * writing to the the metric's storage engine before returning a value.
    * This function will not wait for data from child processes.
    *
    * This doesn't clear the stored value.
    * Parent process only. Panics in child processes.
    *
+   * @param aPingName The (optional) name of the ping to retrieve the metric
+   *        for. Defaults to the first value in `send_in_pings`.
+   *
    * @return value of the stored metric, or Nothing() if there is no value.
    */
-  Maybe<nsCString> TestGetValue(const nsACString& aStorageName) const {
-    if (!fog_string_test_has_value(mId, &aStorageName)) {
+  Maybe<nsCString> TestGetValue(
+      const nsACString& aPingName = nsCString()) const {
+    if (!fog_string_test_has_value(mId, &aPingName)) {
       return Nothing();
     }
     nsCString ret;
-    fog_string_test_get_value(mId, &aStorageName, &ret);
+    fog_string_test_get_value(mId, &aPingName, &ret);
     return Some(ret);
   }
 
  private:
   const uint32_t mId;
 };
 }  // namespace impl
 

--- a/toolkit/components/glean/bindings/private/Timespan.h
+++ b/toolkit/components/glean/bindings/private/Timespan.h
@@ -45,23 +45,26 @@ class TimespanMetric {
    *
    * This function will attempt to await the last parent-process task (if any)
    * writing to the the metric's storage engine before returning a value.
    * This function will not wait for data from child processes.
    *
    * This doesn't clear the stored value.
    * Parent process only. Panics in child processes.
    *
+   * @param aPingName The (optional) name of the ping to retrieve the metric
+   *        for. Defaults to the first value in `send_in_pings`.
+   *
    * @return value of the stored metric, or Nothing() if there is no value.
    */
-  Maybe<int64_t> TestGetValue(const nsACString& aStorageName) const {
-    if (!fog_timespan_test_has_value(mId, &aStorageName)) {
+  Maybe<int64_t> TestGetValue(const nsACString& aPingName = nsCString()) const {
+    if (!fog_timespan_test_has_value(mId, &aPingName)) {
       return Nothing();
     }
-    return Some(fog_timespan_test_get_value(mId, &aStorageName));
+    return Some(fog_timespan_test_get_value(mId, &aPingName));
   }
 
  private:
   const uint32_t mId;
 };
 }  // namespace impl
 
 class GleanTimespan final : public nsIGleanTimespan {

--- a/toolkit/components/glean/bindings/private/Uuid.h
+++ b/toolkit/components/glean/bindings/private/Uuid.h
@@ -38,26 +38,29 @@ class UuidMetric {
    * Gets the currently stored value as a hyphenated string.
    *
    * This function will attempt to await the last parent-process task (if any)
    * writing to the the metric's storage engine before returning a value.
    * This function will not wait for data from child processes.
    *
    * This doesn't clear the stored value.
    * Parent process only. Panics in child processes.
-   * Panics if there is no value to get.
+   *
+   * @param aPingName The (optional) name of the ping to retrieve the metric
+   *        for. Defaults to the first value in `send_in_pings`.
    *
    * @return value of the stored metric, or Nothing() if there is no value.
    */
-  Maybe<nsCString> TestGetValue(const nsACString& aStorageName) const {
-    if (!fog_uuid_test_has_value(mId, &aStorageName)) {
+  Maybe<nsCString> TestGetValue(
+      const nsACString& aPingName = nsCString()) const {
+    if (!fog_uuid_test_has_value(mId, &aPingName)) {
       return Nothing();
     }
     nsCString ret;
-    fog_uuid_test_get_value(mId, &aStorageName, &ret);
+    fog_uuid_test_get_value(mId, &aPingName, &ret);
     return Some(ret);
   }
 
  private:
   const uint32_t mId;
 };
 }  // namespace impl
 

--- a/toolkit/components/glean/gtest/TestFog.cpp
+++ b/toolkit/components/glean/gtest/TestFog.cpp
@@ -58,16 +58,18 @@ TEST(FOG, BuiltinPingsRegistered)
 
 TEST(FOG, TestCppCounterWorks)
 {
   mozilla::glean::test_only::bad_code.Add(42);
 
   ASSERT_EQ(
       42,
       mozilla::glean::test_only::bad_code.TestGetValue("test-ping"_ns).value());
+  // And test that the ping name's optional, while you're at it:
+  ASSERT_EQ(42, test_only::bad_code.TestGetValue().value());
 }
 
 TEST(FOG, TestCppStringWorks)
 {
   auto kValue = "cheez!"_ns;
   mozilla::glean::test_only::cheesy_string.Set(kValue);
 
   ASSERT_STREQ(kValue.get(), mozilla::glean::test_only::cheesy_string

--- a/toolkit/components/glean/xpcom/nsIGleanMetrics.idl
+++ b/toolkit/components/glean/xpcom/nsIGleanMetrics.idl
@@ -22,19 +22,22 @@ interface nsIGleanBoolean : nsISupports
    *
    * This function will attempt to await the last parent-process task (if any)
    * writing to the the metric's storage engine before returning a value.
    * This function will not wait for data from child processes.
    *
    * This doesn't clear the stored value.
    * Parent process only. Panics in child processes.
    *
+   * @param aPingName The (optional) name of the ping to retrieve the metric
+   *        for. Defaults to the first value in `send_in_pings`.
+   *
    * @return value of the stored metric, or undefined if there is no value.
    */
-  jsval testGetValue(in AUTF8String aStorageName);
+  jsval testGetValue([optional] in AUTF8String aPingName);
 };
 
 [scriptable, uuid(aa15fd20-1e8a-11eb-9bec-0800200c9a66)]
 interface nsIGleanDatetime : nsISupports
 {
   /**
    * Set the datetime to the provided value, or the local now.
    *
@@ -50,20 +53,23 @@ interface nsIGleanDatetime : nsISupports
    *
    * This function will attempt to await the last parent-process task (if any)
    * writing to the the metric's storage engine before returning a value.
    * This function will not wait for data from child processes.
    *
    * This doesn't clear the stored value.
    * Parent process only. Panics in child processes.
    *
+   * @param aPingName The (optional) name of the ping to retrieve the metric
+   *        for. Defaults to the first value in `send_in_pings`.
+   *
    * @return value of the stored metric, or undefined if there is no value.
    */
   [implicit_jscontext]
-  jsval testGetValue(in AUTF8String aStorageName);
+  jsval testGetValue([optional] in AUTF8String aPingName);
 };
 
 [scriptable, uuid(05b89d2a-d57c-11ea-82da-3f63399a6f5a)]
 interface nsIGleanCounter : nsISupports
 {
   /*
   * Increases the counter by `amount`.
   *
@@ -78,19 +84,22 @@ interface nsIGleanCounter : nsISupports
    *
    * This function will attempt to await the last parent-process task (if any)
    * writing to the the metric's storage engine before returning a value.
    * This function will not wait for data from child processes.
    *
    * This doesn't clear the stored value.
    * Parent process only. Panics in child processes.
    *
+   * @param aPingName The (optional) name of the ping to retrieve the metric
+   *        for. Defaults to the first value in `send_in_pings`.
+   *
    * @return value of the stored metric, or undefined if there is no value.
    */
-  jsval testGetValue(in AUTF8String aStorageName);
+  jsval testGetValue([optional] in AUTF8String aPingName);
 };
 
 [scriptable, uuid(eea5ed46-16ba-46cd-bb1f-504581987fe1)]
 interface nsIGleanMemoryDistribution : nsISupports
 {
   /*
    * Accumulates the provided sample in the metric.
    *
@@ -109,20 +118,23 @@ interface nsIGleanMemoryDistribution : n
    *
    * This function will attempt to await the last parent-process task (if any)
    * writing to the the metric's storage engine before returning a value.
    * This function will not wait for data from child processes.
    *
    * This doesn't clear the stored value.
    * Parent process only. Panics in child processes.
    *
+   * @param aPingName The (optional) name of the ping to retrieve the metric
+   *        for. Defaults to the first value in `send_in_pings`.
+   *
    * @return value of the stored metric, or Nothing() if there is no value.
    */
   [implicit_jscontext]
-	jsval testGetValue(in ACString aStorageName);
+	jsval testGetValue([optional] in ACString aPingName);
 };
 
 [scriptable, uuid(5223a48b-687d-47ff-a629-fd4a72d1ecfa)]
 interface nsIGleanPing : nsISupports
 {
   /**
    * Collect and submit the ping for eventual upload.
    *
@@ -162,20 +174,23 @@ interface nsIGleanString : nsISupports
    *
    * This function will attempt to await the last parent-process task (if any)
    * writing to the the metric's storage engine before returning a value.
    * This function will not wait for data from child processes.
    *
    * This doesn't clear the stored value.
    * Parent process only. Panics in child processes.
    *
+   * @param aPingName The (optional) name of the ping to retrieve the metric
+   *        for. Defaults to the first value in `send_in_pings`.
+   *
    * @return value of the stored metric, or undefined if there is no value.
    */
   [implicit_jscontext]
-  jsval testGetValue(in AUTF8String aStorageName);
+  jsval testGetValue([optional] in AUTF8String aPingName);
 };
 
 [scriptable, uuid(2586530c-030f-11eb-93cb-cbf30d25225a)]
 interface nsIGleanTimespan : nsISupports
 {
   /**
    * Start tracking time for the provided metric.
    *
@@ -202,19 +217,22 @@ interface nsIGleanTimespan : nsISupports
    *
    * This function will attempt to await the last parent-process task (if any)
    * writing to the the metric's storage engine before returning a value.
    * This function will not wait for data from child processes.
    *
    * This doesn't clear the stored value.
    * Parent process only. Panics in child processes.
    *
+   * @param aPingName The (optional) name of the ping to retrieve the metric
+   *        for. Defaults to the first value in `send_in_pings`.
+   *
    * @return value of the stored metric, or undefined if there is no value.
    */
-  jsval testGetValue(in AUTF8String aStorageName);
+  jsval testGetValue([optional] in AUTF8String aPingName);
 };
 
 [scriptable, uuid(395700e7-06f6-46be-adcc-ea58977fda6d)]
 interface nsIGleanUuid : nsISupports
 {
   /**
    * Set to the specified value.
    *
@@ -234,20 +252,23 @@ interface nsIGleanUuid : nsISupports
    *
    * This function will attempt to await the last parent-process task (if any)
    * writing to the the metric's storage engine before returning a value.
    * This function will not wait for data from child processes.
    *
    * This doesn't clear the stored value.
    * Parent process only. Panics in child processes.
    *
+   * @param aPingName The (optional) name of the ping to retrieve the metric
+   *        for. Defaults to the first value in `send_in_pings`.
+   *
    * @return value of the stored metric, or undefined if there is no value.
    */
   [implicit_jscontext]
-  jsval testGetValue(in AUTF8String aStorageName);
+  jsval testGetValue([optional] in AUTF8String aPingName);
 };
 
 [scriptable, uuid(1b01424a-1f55-11eb-92a5-0754f6c3f240)]
 interface nsIGleanEvent : nsISupports
 {
   /*
    * Record an event.
    *
@@ -263,13 +284,16 @@ interface nsIGleanEvent : nsISupports
    *
    * This function will attempt to await the last parent-process task (if any)
    * writing to the the metric's storage engine before returning a value.
    * This function will not wait for data from child processes.
    *
    * This doesn't clear the stored value.
    * Parent process only. Panics in child processes.
    *
+   * @param aPingName The (optional) name of the ping to retrieve the metric
+   *        for. Defaults to the first value in `send_in_pings`.
+   *
    * @return value of the stored metric.
    */
   [implicit_jscontext]
-  jsval testGetValue(in AUTF8String aStorageName);
+  jsval testGetValue([optional] in AUTF8String aPingName);
 };

--- a/toolkit/components/glean/xpcshell/test_Glean.js
+++ b/toolkit/components/glean/xpcshell/test_Glean.js
@@ -130,16 +130,18 @@ add_task({ skip_if: () => true }, functi
 
   const received = Glean.test_only.what_a_date.testGetValue("test-ping");
   Assert.ok(received.startsWith("2020-06-11T12:00:00"));
 });
 
 add_task(function test_fog_boolean_works() {
   Glean.test_only.can_we_flag_it.set(false);
   Assert.equal(false, Glean.test_only.can_we_flag_it.testGetValue("test-ping"));
+  // While you're here, might as well test that the ping name's optional.
+  Assert.equal(false, Glean.test_only.can_we_flag_it.testGetValue());
 });
 
 add_task(async function test_fog_event_works() {
   Glean.test_only_ipc.no_extra_event.record();
   // FIXME(bug 1678567): Check that the value was recorded when we can.
   // Assert.ok(Glean.test_only_ipc.no_extra_event.testGetValue("store1"));
 
   let extra = { extra1: "can set extras", extra2: "passing more data" };