[GCP Observability C++] Add empty config test (#32790)

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src/cpp/ext/gcp/observability_config.cc

@@ -55,7 +55,7 @@ absl::StatusOr<std::string> GetGcpObservabilityConfigContents() {
   // First, try GRPC_GCP_OBSERVABILITY_CONFIG_FILE
   std::string contents_str;
   auto path = grpc_core::GetEnv("GRPC_GCP_OBSERVABILITY_CONFIG_FILE");
-  if (path.has_value()) {
+  if (path.has_value() && !path.value().empty()) {
     grpc_slice contents;
     grpc_error_handle error =
         grpc_load_file(path->c_str(), /*add_null_terminator=*/true, &contents);
@@ -70,7 +70,7 @@ absl::StatusOr<std::string> GetGcpObservabilityConfigContents() {
   }
   // Next, try GRPC_GCP_OBSERVABILITY_CONFIG env var.
   auto env_config = grpc_core::GetEnv("GRPC_GCP_OBSERVABILITY_CONFIG");
-  if (env_config.has_value()) {
+  if (env_config.has_value() && !env_config.value().empty()) {
     return std::move(*env_config);
   }
   // No observability config found.

test/cpp/ext/gcp/observability_config_test.cc

@@ -409,6 +409,22 @@ TEST_P(EnvParsingTest, BadJson) {
       << config.status().message();
 }
 
+TEST_P(EnvParsingTest, BadJsonEmptyString) {
+  SetConfig("");
+  auto config = GcpObservabilityConfig::ReadFromEnv();
+  if (GetParam().config_source() == EnvParsingTestType::ConfigSource::kFile) {
+    EXPECT_EQ(config.status().code(), absl::StatusCode::kInvalidArgument);
+    EXPECT_THAT(config.status().message(),
+                ::testing::HasSubstr("JSON parsing failed"))
+        << config.status().message();
+  } else {
+    EXPECT_EQ(config.status(),
+              absl::FailedPreconditionError(
+                  "Environment variables GRPC_GCP_OBSERVABILITY_CONFIG_FILE or "
+                  "GRPC_GCP_OBSERVABILITY_CONFIG not defined"));
+  }
+}
+
 // Make sure that GCP config errors are propagated as expected.
 TEST_P(EnvParsingTest, BadGcpConfig) {
   SetConfig(R"json({