diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 1668b816f8ae5f88a920925fd4e6e00f333f1bb2..e16e20a2378830a2a792c94db732fda93509120f 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -745,6 +745,97 @@ gcc_8_mpionly:
 gcc_8_hybrid:
    <<: *build_definition
    image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc:8
+   variables:
+      <<: *build_hybrid_variables
+      WALBERLA_BUILD_WITH_CUDA: "OFF"
+      WALBERLA_ENABLE_GUI: 0
+   only:
+      variables:
+         - $ENABLE_NIGHTLY_BUILDS
+   tags:
+      - docker
+
+gcc_8_serial_dbg:
+   <<: *build_definition
+   image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc:8
+   variables:
+      <<: *build_serial_dbg_variables
+      WALBERLA_BUILD_WITH_CUDA: "OFF"
+      WALBERLA_ENABLE_GUI: 0
+   only:
+      variables:
+         - $ENABLE_NIGHTLY_BUILDS
+   tags:
+      - docker
+
+gcc_8_mpionly_dbg:
+   <<: *build_definition
+   image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc:8
+   variables:
+      <<: *build_mpionly_dbg_variables
+      WALBERLA_BUILD_WITH_CUDA: "OFF"
+      WALBERLA_ENABLE_GUI: 0
+   only:
+      variables:
+         - $ENABLE_NIGHTLY_BUILDS
+   tags:
+      - docker
+
+gcc_8_hybrid_dbg:
+   <<: *build_definition
+   image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc:8
+   variables:
+      <<: *build_hybrid_dbg_variables
+      WALBERLA_BUILD_WITH_CUDA: "OFF"
+      WALBERLA_ENABLE_GUI: 0
+   only:
+      variables:
+         - $ENABLE_NIGHTLY_BUILDS
+   tags:
+      - docker
+
+gcc_8_hybrid_dbg_sp:
+   <<: *build_definition
+   image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc:8
+   variables:
+      <<: *build_hybrid_dbg_sp_variables
+      WALBERLA_BUILD_WITH_CUDA: "OFF"
+      WALBERLA_ENABLE_GUI: 0
+   only:
+      variables:
+         - $ENABLE_NIGHTLY_BUILDS
+   tags:
+      - docker
+
+gcc_9_serial:
+   <<: *build_definition
+   image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc:9
+   variables:
+      <<: *build_serial_variables
+      WALBERLA_BUILD_WITH_CUDA: "OFF"
+      WALBERLA_ENABLE_GUI: 0
+   only:
+      variables:
+         - $ENABLE_NIGHTLY_BUILDS
+   tags:
+      - docker
+
+gcc_9_mpionly:
+   <<: *build_definition
+   image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc:9
+   variables:
+      <<: *build_mpionly_variables
+      WALBERLA_BUILD_WITH_CUDA: "OFF"
+      WALBERLA_ENABLE_GUI: 0
+   only:
+      variables:
+         - $ENABLE_NIGHTLY_BUILDS
+   tags:
+      - docker
+
+gcc_9_hybrid:
+   <<: *build_definition
+   image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc:9
    stage: pretest
    variables:
       <<: *build_hybrid_variables
@@ -756,9 +847,9 @@ gcc_8_hybrid:
    tags:
       - docker
 
-gcc_8_serial_dbg:
+gcc_9_serial_dbg:
    <<: *build_definition
-   image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc:8
+   image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc:9
    variables:
       <<: *build_serial_dbg_variables
       WALBERLA_BUILD_WITH_CUDA: "OFF"
@@ -769,9 +860,9 @@ gcc_8_serial_dbg:
    tags:
       - docker
 
-gcc_8_mpionly_dbg:
+gcc_9_mpionly_dbg:
    <<: *build_definition
-   image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc:8
+   image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc:9
    variables:
       <<: *build_mpionly_dbg_variables
       WALBERLA_BUILD_WITH_CUDA: "OFF"
@@ -782,9 +873,9 @@ gcc_8_mpionly_dbg:
    tags:
       - docker
 
-gcc_8_hybrid_dbg:
+gcc_9_hybrid_dbg:
    <<: *build_definition
-   image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc:8
+   image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc:9
    variables:
       <<: *build_hybrid_dbg_variables
       WALBERLA_BUILD_WITH_CUDA: "OFF"
@@ -795,9 +886,9 @@ gcc_8_hybrid_dbg:
    tags:
       - docker
 
-gcc_8_hybrid_dbg_sp:
+gcc_9_hybrid_dbg_sp:
    <<: *build_definition
-   image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc:8
+   image: i10git.cs.fau.de:5005/walberla/buildenvs/gcc:9
    variables:
       <<: *build_hybrid_dbg_sp_variables
       WALBERLA_BUILD_WITH_CUDA: "OFF"
@@ -1786,4 +1877,4 @@ benchmark_gcc8:
 
 benchmark_clang8:
    <<: *benchmark_definition
-   image: i10git.cs.fau.de:5005/walberla/buildenvs/clang:8.0
+   image: i10git.cs.fau.de:5005/walberla/buildenvs/clang:8.0
\ No newline at end of file
diff --git a/src/blockforest/BlockID.h b/src/blockforest/BlockID.h
index dddb36d96c9659d9e7e8d6460c5bfd939726fe78..9a28bc690cdeddbac83a206704a3eb41359bede1 100644
--- a/src/blockforest/BlockID.h
+++ b/src/blockforest/BlockID.h
@@ -260,8 +260,8 @@ class BlockID : public IBlockID {
 
 public:
 
-   inline BlockID() : id_( uint_c(0) ) {}
-   inline BlockID( const BlockID& id ) : id_( id.id_ ) {}
+   inline BlockID() = default;
+   inline BlockID( const BlockID& id ) = default;
    inline BlockID( const uint_t id ) : id_( id ) {}
    inline BlockID( const uint_t treeIndex, const uint_t treeIdMarker );
    inline BlockID( const BlockID& id, const uint_t branchId );
@@ -302,7 +302,7 @@ public:
 
 private:
 
-   uint_t id_;
+   uint_t id_ = uint_c(0);
 
 }; // class BlockID