diff --git a/arebac-core/src/main/java/io/github/danthe1st/arebac/gpeval/GPEval.java b/arebac-core/src/main/java/io/github/danthe1st/arebac/gpeval/GPEval.java
index 7547529..b5be8ae 100644
--- a/arebac-core/src/main/java/io/github/danthe1st/arebac/gpeval/GPEval.java
+++ b/arebac-core/src/main/java/io/github/danthe1st/arebac/gpeval/GPEval.java
@@ -15,8 +15,8 @@
 import io.github.danthe1st.arebac.data.commongraph.attributed.AttributeAware;
 import io.github.danthe1st.arebac.data.commongraph.attributed.AttributeValue;
 import io.github.danthe1st.arebac.data.commongraph.attributed.AttributeValue.StringAttribute;
-import io.github.danthe1st.arebac.data.commongraph.attributed.AttributedGraph;
 import io.github.danthe1st.arebac.data.commongraph.attributed.AttributedEdge;
+import io.github.danthe1st.arebac.data.commongraph.attributed.AttributedGraph;
 import io.github.danthe1st.arebac.data.commongraph.attributed.AttributedNode;
 import io.github.danthe1st.arebac.data.graph_pattern.GPEdge;
 import io.github.danthe1st.arebac.data.graph_pattern.GPNode;
@@ -312,7 +312,9 @@ private GPNode pickNextNode() {
 				numberOfPossibilities = possibilities;
 			}
 		}
-		Objects.requireNonNull(candidate);
+		if (candidate == null) {
+			throw new IllegalStateException("No candidate node found. Make sure all nodes in the graph pattern are have some connection to a fixed node.");
+		}
 		return candidate;
 	}
 
diff --git a/arebac-core/src/test/java/io/github/danthe1st/arebac/tests/gpeval/NotConnectedToFixedNodeTest.java b/arebac-core/src/test/java/io/github/danthe1st/arebac/tests/gpeval/NotConnectedToFixedNodeTest.java
new file mode 100644
index 0000000..a764f48
--- /dev/null
+++ b/arebac-core/src/test/java/io/github/danthe1st/arebac/tests/gpeval/NotConnectedToFixedNodeTest.java
@@ -0,0 +1,73 @@
+package io.github.danthe1st.arebac.tests.gpeval;
+
+import static io.github.danthe1st.arebac.data.commongraph.attributed.AttributeValue.attribute;
+import static io.github.danthe1st.arebac.data.graph_pattern.constraints.AttributeRequirement.ID_KEY;
+import static io.github.danthe1st.arebac.data.graph_pattern.constraints.AttributeRequirementOperator.EQUAL;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import io.github.danthe1st.arebac.data.graph_pattern.GPGraph;
+import io.github.danthe1st.arebac.data.graph_pattern.GPNode;
+import io.github.danthe1st.arebac.data.graph_pattern.GraphPattern;
+import io.github.danthe1st.arebac.data.graph_pattern.constraints.AttributeRequirement;
+import io.github.danthe1st.arebac.data.memory.InMemoryGraph;
+import io.github.danthe1st.arebac.data.memory.InMemoryGraphNode;
+import io.github.danthe1st.arebac.gpeval.GPEval;
+import org.junit.jupiter.api.Test;
+
+class NotConnectedToFixedNodeTest {
+	@Test
+	void testGPGraphWithoutFixedNode() {
+		GraphPattern pattern = createGraphPatternWithSingleNonFixedNode();
+		InMemoryGraph targetGraph = new InMemoryGraph(List.of(new InMemoryGraphNode("a", "NODE", Map.of())), List.of());
+		
+		assertThrows(IllegalStateException.class, () -> GPEval.evaluate(targetGraph, pattern), "No candidate node found. Make sure all nodes in the graph pattern are have some connection to a fixed node.");
+	}
+	
+	@Test
+	void testGPGraphWithoutFixedNodeOnEmptyTargetGraph() {
+		GraphPattern pattern = createGraphPatternWithSingleNonFixedNode();
+		InMemoryGraph targetGraph = new InMemoryGraph(List.of(), List.of());
+		
+		assertThrows(IllegalStateException.class, () -> GPEval.evaluate(targetGraph, pattern), "No candidate node found. Make sure all nodes in the graph pattern are have some connection to a fixed node.");
+	}
+
+	private GraphPattern createGraphPatternWithSingleNonFixedNode() {
+		GPNode node = new GPNode("nId", "NODE");
+		GPGraph graph = new GPGraph(List.of(node), List.of());
+		return new GraphPattern(graph, List.of(), Map.of(), Map.of(), List.of(node), Map.of());
+	}
+	
+	@Test
+	void testGPGraphWithoutConnectionToFixedNode() {
+		GraphPattern pattern = createGraphPatternWithFixedNodeAndUnconnectedNode();
+		InMemoryGraph targetGraph = new InMemoryGraph(List.of(), List.of());
+		
+		// if a fixed node cannot be found, the result is the empty set
+		Set<List<InMemoryGraphNode>> result = GPEval.evaluate(targetGraph, pattern);
+		assertEquals(Set.of(), result);
+	}
+	
+	@Test
+	void testGPGraphWithoutConnectionToFixedNodeNoNodesInGraph() {
+		GraphPattern pattern = createGraphPatternWithFixedNodeAndUnconnectedNode();
+		InMemoryGraph targetGraph = new InMemoryGraph(List.of(new InMemoryGraphNode("FIXED_NODE", "NODE", Map.of()), new InMemoryGraphNode("otherNode", "NODE", Map.of())), List.of());
+		
+		assertThrows(IllegalStateException.class, () -> GPEval.evaluate(targetGraph, pattern), "No candidate node found. Make sure all nodes in the graph pattern are have some connection to a fixed node.");
+	}
+	
+	private GraphPattern createGraphPatternWithFixedNodeAndUnconnectedNode() {
+		GPNode fixedNode = new GPNode("nId", "NODE");
+		GPNode unconnectedNode = new GPNode("otherId", "NODE");
+		GPGraph graph = new GPGraph(List.of(fixedNode, unconnectedNode), List.of());
+		return new GraphPattern(
+				graph, List.of(), Map.of(
+						fixedNode, List.of(new AttributeRequirement(ID_KEY, EQUAL, attribute("FIXED_NODE")))
+				), Map.of(), List.of(unconnectedNode), Map.of()
+		);
+	}
+}