fix(model-client): do not create an empty version when making no changes on branch

Author: Oleksandr Dzhychko

model-client/src/commonMain/kotlin/org/modelix/model/client2/ModelClientV2.kt

@@ -542,6 +542,9 @@ suspend fun <T> IModelClientV2.runWriteOnBranch(branchRef: BranchReference, body
         body(branch)
     }
     val (ops, newTree) = branch.getPendingChanges()
+    if (ops.isEmpty()) {
+        return result
+    }
     val newVersion = CLVersion.createRegularVersion(
         id = client.getIdGenerator().generate(),
         author = client.getUserId(),

model-server/src/test/kotlin/org/modelix/model/server/ModelClientV2Test.kt

@@ -29,6 +29,7 @@ import org.modelix.model.api.ITree
 import org.modelix.model.api.PBranch
 import org.modelix.model.client2.ModelClientV2
 import org.modelix.model.client2.runWrite
+import org.modelix.model.client2.runWriteOnBranch
 import org.modelix.model.lazy.CLTree
 import org.modelix.model.lazy.CLVersion
 import org.modelix.model.lazy.RepositoryId
@@ -216,4 +217,24 @@ class ModelClientV2Test {
         }
         checkAllReferencedEntriesExistInStore(versionPulled.data!!)
     }
+
+    @Test
+    fun `writing no data does not create empty versions`() = runTest {
+        // Arrange
+        val url = "http://localhost/v2"
+        val modelClient = ModelClientV2.builder().url(url).client(client).build().also { it.init() }
+        val repositoryId = RepositoryId("repo1")
+        val branchId = repositoryId.getBranchReference("master")
+        modelClient.initRepository(repositoryId)
+        val versionAfterBeforeWrite = modelClient.pullIfExists(branchId)!!
+
+        // Act
+        modelClient.runWriteOnBranch(branchId) {
+            // do nothing
+        }
+
+        // Assert
+        val versionAfterRunWrite = modelClient.pullIfExists(branchId)!!
+        assertEquals(versionAfterBeforeWrite.getContentHash(), versionAfterRunWrite.getContentHash())
+    }
 }