Fix another place where type could be nil

extractor/extractor.go

@@ -940,11 +940,19 @@ func extractExpr(tw *trap.Writer, expr ast.Expr, parent trap.Label, idx int) {
 		if expr == nil {
 			return
 		}
-		if _, ok := typeOf(tw, expr.X).Underlying().(*types.Signature); ok {
+		typeofx := typeOf(tw, expr.X)
+		if typeofx == nil {
+			// We are missing type information for `expr.X`, so we cannot
+			// determine whether this is a generic function instantiation
+			// or not.
+			kind = dbscheme.GenericTypeInstantiationExpr.Index()
+		} else {
+			if _, ok := typeofx.Underlying().(*types.Signature); ok {
 				kind = dbscheme.GenericFunctionInstantiationExpr.Index()
 			} else {
 				kind = dbscheme.GenericTypeInstantiationExpr.Index()
 			}
+		}
 		extractExpr(tw, expr.X, lbl, 0)
 		extractExprs(tw, expr.Indices, lbl, 1, 1)
 	case *ast.SliceExpr: