fix(gui): resolve NPE during index (#1254)

jadx-core/src/main/java/jadx/api/JadxDecompiler.java

@@ -538,7 +538,11 @@ public final class JadxDecompiler implements Closeable {
 		}
 		if (obj instanceof VariableNode) {
 			VariableNode varNode = (VariableNode) obj;
-			return new JavaVariable(getJavaClassByNode(varNode.getClassNode().getTopParentClass()), varNode);
+			JavaClass javaCls = getJavaClassByNode(varNode.getClassNode().getTopParentClass());
+			if (javaCls == null) {
+				return null;
+			}
+			return new JavaVariable(javaCls, varNode);
 		}
 		throw new JadxRuntimeException("Unexpected node type: " + obj);
 	}

jadx-core/src/main/java/jadx/api/JavaVariable.java

@@ -2,16 +2,17 @@ package jadx.api;
 
 import java.util.Collections;
 import java.util.List;
+import java.util.Objects;
 
 import jadx.core.dex.nodes.VariableNode;
 
 public class JavaVariable implements JavaNode {
-	JavaClass cls;
-	VariableNode node;
+	private final JavaClass cls;
+	private final VariableNode node;
 
 	public JavaVariable(JavaClass cls, VariableNode node) {
-		this.cls = cls;
-		this.node = node;
+		this.cls = Objects.requireNonNull(cls);
+		this.node = Objects.requireNonNull(node);
 	}
 
 	public VariableNode getVariableNode() {