move default label to constant

src/main/java/kieker/analysis/graph/BlueprintsExporter.java

@@ -11,6 +11,8 @@ public class BlueprintsExporter {
 	private final com.tinkerpop.blueprints.Graph exportGraph = new TinkerGraph();
 	private final Map<Vertex, com.tinkerpop.blueprints.Vertex> mappedVertices = new HashMap<>();
 
+	private static final String LABEL_PROPERTY = "label";
+
 	public BlueprintsExporter(final Graph graph) {
 		this.graph = graph;
 	}
@@ -41,7 +43,7 @@ public class BlueprintsExporter {
 		for (final Edge edge : graph.getEdges()) {
 			final com.tinkerpop.blueprints.Vertex mappedInVertex = mappedVertices.get(edge.getVertex(Direction.IN));
 			final com.tinkerpop.blueprints.Vertex mappedOutVertex = mappedVertices.get(edge.getVertex(Direction.OUT));
-			String label = edge.getProperty("label");
+			String label = edge.getProperty(LABEL_PROPERTY);
 			if (label == null) {
 				label = "";
 			}