fix: conditional run matrix (#129)

throws error if matrix is empty, prevent that with if check

.github/workflows/preset-image-build.yml

@@ -47,12 +47,13 @@ jobs:
 
       - name: Get Modified files
         run: |
-          git fetch origin main
+          git checkout --detach
+          git fetch origin main:main
           current_branch=$(git rev-parse --abbrev-ref HEAD)
           if [ "$current_branch" == "main" ] || [ "$current_branch" == "master" ]; then
             files=$(git diff --name-only HEAD^ HEAD)
           else
-              files=$(git diff --name-only main...HEAD)
+              files=$(git diff --name-only origin/main...HEAD)
           fi
           echo "Modified files: $files"
           FILES_MODIFIED=""
@@ -139,6 +140,7 @@ jobs:
     runs-on: self-hosted
     outputs:
       matrix: ${{ steps.set_matrix.outputs.matrix }}
+      matrix_empty: ${{ steps.set_matrix.outputs.matrix_empty }}
     steps:
     - name: Checkout
       uses: actions/checkout@v4
@@ -151,12 +153,19 @@ jobs:
       run: |
         matrix=$(jq --arg FALCON_MODIFIED "${{ needs.setup.outputs.FALCON_MODIFIED }}" --arg LLAMA2_MODIFIED "${{ needs.setup.outputs.LLAMA2_MODIFIED }}" --arg LLAMA2_CHAT_MODIFIED "${{ needs.setup.outputs.LLAMA2_CHAT_MODIFIED }}" 'map( 
             . | select((.shouldBuildFalcon == $FALCON_MODIFIED) or (.shouldBuildLlama2 == $LLAMA2_MODIFIED) or (.shouldBuildLlama2Chat == $LLAMA2_CHAT_MODIFIED))
-        )' .github/matrix-configs.json) 
+        )' .github/matrix-configs.json)
+        # Check if matrix is empty and set an output variable
+        if [[ $matrix == "[]" ]]; then
+          echo "matrix_empty=true" >> $GITHUB_OUTPUT
+        else
+          echo "matrix_empty=false" >> $GITHUB_OUTPUT
+        fi
         echo "matrix={\"include\":$(echo $matrix)}" >> $GITHUB_OUTPUT
 
   build-models: 
     needs: [setup, matrix_prep]
     runs-on: self-hosted
+    if: ${{needs.matrix_prep.outputs.matrix_empty == 'false'}}
     strategy:
       fail-fast: false
       matrix: ${{fromJson(needs.matrix_prep.outputs.matrix)}}