[1194] Fix empty diagram svg export

Bug: #1194
Signed-off-by: Guillaume Coutable <[email protected]>

CHANGELOG.adoc

@@ -40,6 +40,7 @@ See ADR-54 for the details.
 - https://github.com/eclipse-sirius/sirius-components/issues/1171[#1171] [workbench] Fix the overflow behavior of the side panels when they are resized horizontally
 - https://github.com/eclipse-sirius/sirius-components/issues/1115[#1115] [workbench] Stop using the deprecated props `rowsMax`
 - https://github.com/eclipse-sirius/sirius-components/issues/1195[#1195] [diagram] Fix edge svg export
+- https://github.com/eclipse-sirius/sirius-components/issues/1194[#1194] [diagram] Fix empty diagram svg export
 
 === Improvements
 

backend/sirius-components-collaborative-diagrams/src/main/java/org/eclipse/sirius/components/collaborative/diagrams/export/svg/DiagramExportService.java

@@ -124,10 +124,10 @@ private StringBuilder computeViewBox(Diagram diagram) {
 
         this.computeElementsCoordinates(diagram);
 
-        double minX = this.xBeginPositions.stream().min(Double::compare).get();
-        double minY = this.yBeginPositions.stream().min(Double::compare).get();
-        double maxX = this.xEndPositions.stream().max(Double::compare).get();
-        double maxY = this.yEndPositions.stream().max(Double::compare).get();
+        double minX = this.xBeginPositions.stream().min(Double::compare).orElse(0d);
+        double minY = this.yBeginPositions.stream().min(Double::compare).orElse(0d);
+        double maxX = this.xEndPositions.stream().max(Double::compare).orElse(0d);
+        double maxY = this.yEndPositions.stream().max(Double::compare).orElse(0d);
 
         int padding = 20;
         double width = Math.abs(minX - maxX) + diagram.getPosition().getX();

backend/sirius-components-collaborative-diagrams/src/test/java/org/eclipse/sirius/components/collaborative/diagrams/export/DiagramExportServiceTests.java

@@ -72,4 +72,12 @@ public void testExportDiagramWithEdge() throws URISyntaxException {
         assertThat(export).contains("<path d=\""); //$NON-NLS-1$
     }
 
+    @Test
+    public void testExportEmptyDiagram() throws URISyntaxException {
+        Diagram emptyDiagram = TestLayoutDiagramBuilder.diagram("Root").nodes().and().build(); //$NON-NLS-1$
+        DiagramExportService diagramExportService = this.getDiagramExportService();
+        String export = diagramExportService.export(emptyDiagram);
+        assertThat(export).isNotBlank();
+    }
+
 }