Fix empty query when using --excludeExternalTargets with --useCquery

cli/src/main/kotlin/com/bazel_diff/bazel/BazelClient.kt

@@ -35,9 +35,13 @@ class BazelClient(
           // In addition, we must include all source dependencies in this query in order for them to
           // show up in
           // `configuredRuleInput`. Hence, one must not filter them out with `kind(rule, deps(..))`.
-          (queryService.query("deps(//...:all-targets)", useCquery = true) +
-                  queryService.query(repoTargetsQuery.joinToString(" + ") { "'$it'" }))
-              .distinctBy { it.name }
+          val mainTargets = queryService.query("deps(//...:all-targets)", useCquery = true)
+          val repoTargets = if (repoTargetsQuery.isNotEmpty()) {
+            queryService.query(repoTargetsQuery.joinToString(" + ") { "'$it'" })
+          } else {
+            emptyList()
+          }
+          (mainTargets + repoTargets).distinctBy { it.name }
         } else {
           val buildTargetsQuery =
               listOf("//...:all-targets") +

cli/src/test/kotlin/com/bazel_diff/e2e/E2ETest.kt

@@ -587,6 +587,33 @@ class E2ETest {
     assertThat(actual).isEqualTo(expected)
   }
 
+  @Test
+  fun testUseCqueryWithExcludeExternalTargets() {
+    // This test verifies the fix for the issue where using --excludeExternalTargets with --useCquery
+    // would cause an empty query string to be passed to Bazel, resulting in exit code 2.
+    val workingDirectory = extractFixtureProject("/fixture/cquery-test-base.zip")
+
+    val bazelPath = "bazel"
+    val outputDir = temp.newFolder()
+    val hashesJson = File(outputDir, "hashes.json")
+
+    val cli = CommandLine(BazelDiff())
+
+    val exitCode = cli.execute(
+        "generate-hashes",
+        "-w",
+        workingDirectory.absolutePath,
+        "-b",
+        bazelPath,
+        "--useCquery",
+        // Platform is specified only to make the cquery succeed.
+        "--cqueryCommandOptions",
+        "--platforms=//:jre",
+        "--excludeExternalTargets",
+        hashesJson.absolutePath)
+    assertThat(exitCode).isEqualTo(0)
+  }
+
   @Test
   fun testTargetDistanceMetrics() {
     val workspace = copyTestWorkspace("distance_metrics")