fix(model-server): fix master branch appearing in available branches after removal

The empty string got mapped to a BranchReference and resolved to the DEFAULT_BRANCH.

Author: mhuster23

model-server/src/main/kotlin/org/modelix/model/server/handlers/RepositoriesManager.kt

@@ -181,7 +181,7 @@ class RepositoriesManager(val client: LocalModelClient) : IRepositoriesManager {
     }
 
     fun getBranchNames(repositoryId: RepositoryId): Set<String> {
-        return store.getGenericStore()[branchListKey(repositoryId)]?.lines()?.toSet().orEmpty()
+        return store.getGenericStore()[branchListKey(repositoryId)]?.ifEmpty { null }?.lines()?.toSet().orEmpty()
     }
 
     override fun getBranches(repositoryId: RepositoryId): Set<BranchReference> {

model-server/src/test/kotlin/org/modelix/model/server/handlers/RepositoriesManagerTest.kt

@@ -26,6 +26,16 @@ class RepositoriesManagerTest {
         store.close()
     }
 
+    @Test
+    fun `deleting default branch works`() = runTest {
+        val repoId = RepositoryId("branch-removal")
+        initRepository(repoId)
+        repoManager.removeBranches(repoId, setOf("master"))
+        val branches = repoManager.getBranches(repoId)
+
+        assertTrue { branches.none { it.branchName == "master" } }
+    }
+
     @Test
     fun `repository data is removed when removing repository`() = runTest {
         val repoId = RepositoryId("abc")