diff --git a/go/extractor/extractor.go b/go/extractor/extractor.go
index c4544390753..1456dd3a899 100644
--- a/go/extractor/extractor.go
+++ b/go/extractor/extractor.go
@@ -936,7 +936,16 @@ func emitScopeNodeInfo(tw *trap.Writer, nd ast.Node, lbl trap.Label) {
 
 // extractExpr extracts AST information for the given expression and all its subexpressions
 func extractExpr(tw *trap.Writer, expr ast.Expr, parent trap.Label, idx int, skipExtractingValue bool) {
-	if expr == nil {
+	if expr == nil || expr == (*ast.Ident)(nil) || expr == (*ast.BasicLit)(nil) ||
+		expr == (*ast.Ellipsis)(nil) || expr == (*ast.FuncLit)(nil) ||
+		expr == (*ast.CompositeLit)(nil) || expr == (*ast.SelectorExpr)(nil) ||
+		expr == (*ast.IndexListExpr)(nil) || expr == (*ast.SliceExpr)(nil) ||
+		expr == (*ast.TypeAssertExpr)(nil) || expr == (*ast.CallExpr)(nil) ||
+		expr == (*ast.StarExpr)(nil) || expr == (*ast.KeyValueExpr)(nil) ||
+		expr == (*ast.UnaryExpr)(nil) || expr == (*ast.BinaryExpr)(nil) ||
+		expr == (*ast.ArrayType)(nil) || expr == (*ast.StructType)(nil) ||
+		expr == (*ast.FuncType)(nil) || expr == (*ast.InterfaceType)(nil) ||
+		expr == (*ast.MapType)(nil) || expr == (*ast.ChanType)(nil) {
 		return
 	}
 
@@ -948,9 +957,6 @@ func extractExpr(tw *trap.Writer, expr ast.Expr, parent trap.Label, idx int, ski
 	case *ast.BadExpr:
 		kind = dbscheme.BadExpr.Index()
 	case *ast.Ident:
-		if expr == nil {
-			return
-		}
 		kind = dbscheme.IdentExpr.Index()
 		dbscheme.LiteralsTable.Emit(tw, lbl, expr.Name, expr.Name)
 		def := tw.Package.TypesInfo.Defs[expr]
@@ -984,15 +990,9 @@ func extractExpr(tw *trap.Writer, expr ast.Expr, parent trap.Label, idx int, ski
 			}
 		}
 	case *ast.Ellipsis:
-		if expr == nil {
-			return
-		}
 		kind = dbscheme.EllipsisExpr.Index()
 		extractExpr(tw, expr.Elt, lbl, 0, false)
 	case *ast.BasicLit:
-		if expr == nil {
-			return
-		}
 		value := ""
 		switch expr.Kind {
 		case token.INT:
@@ -1016,36 +1016,21 @@ func extractExpr(tw *trap.Writer, expr ast.Expr, parent trap.Label, idx int, ski
 		}
 		dbscheme.LiteralsTable.Emit(tw, lbl, value, expr.Value)
 	case *ast.FuncLit:
-		if expr == nil {
-			return
-		}
 		kind = dbscheme.FuncLitExpr.Index()
 		extractExpr(tw, expr.Type, lbl, 0, false)
 		extractStmt(tw, expr.Body, lbl, 1)
 	case *ast.CompositeLit:
-		if expr == nil {
-			return
-		}
 		kind = dbscheme.CompositeLitExpr.Index()
 		extractExpr(tw, expr.Type, lbl, 0, false)
 		extractExprs(tw, expr.Elts, lbl, 1, 1)
 	case *ast.ParenExpr:
-		if expr == nil {
-			return
-		}
 		kind = dbscheme.ParenExpr.Index()
 		extractExpr(tw, expr.X, lbl, 0, false)
 	case *ast.SelectorExpr:
-		if expr == nil {
-			return
-		}
 		kind = dbscheme.SelectorExpr.Index()
 		extractExpr(tw, expr.X, lbl, 0, false)
 		extractExpr(tw, expr.Sel, lbl, 1, false)
 	case *ast.IndexExpr:
-		if expr == nil {
-			return
-		}
 		typeofx := typeOf(tw, expr.X)
 		if typeofx == nil {
 			// We are missing type information for `expr.X`, so we cannot
@@ -1065,9 +1050,6 @@ func extractExpr(tw *trap.Writer, expr ast.Expr, parent trap.Label, idx int, ski
 		extractExpr(tw, expr.X, lbl, 0, false)
 		extractExpr(tw, expr.Index, lbl, 1, false)
 	case *ast.IndexListExpr:
-		if expr == nil {
-			return
-		}
 		typeofx := typeOf(tw, expr.X)
 		if typeofx == nil {
 			// We are missing type information for `expr.X`, so we cannot
@@ -1084,18 +1066,12 @@ func extractExpr(tw *trap.Writer, expr ast.Expr, parent trap.Label, idx int, ski
 		extractExpr(tw, expr.X, lbl, 0, false)
 		extractExprs(tw, expr.Indices, lbl, 1, 1)
 	case *ast.SliceExpr:
-		if expr == nil {
-			return
-		}
 		kind = dbscheme.SliceExpr.Index()
 		extractExpr(tw, expr.X, lbl, 0, false)
 		extractExpr(tw, expr.Low, lbl, 1, false)
 		extractExpr(tw, expr.High, lbl, 2, false)
 		extractExpr(tw, expr.Max, lbl, 3, false)
 	case *ast.TypeAssertExpr:
-		if expr == nil {
-			return
-		}
 		kind = dbscheme.TypeAssertExpr.Index()
 		extractExpr(tw, expr.X, lbl, 0, false)
 		// expr.Type can be `nil` if this is the `x.(type)` in a type switch.
@@ -1103,9 +1079,6 @@ func extractExpr(tw *trap.Writer, expr ast.Expr, parent trap.Label, idx int, ski
 			extractExpr(tw, expr.Type, lbl, 1, false)
 		}
 	case *ast.CallExpr:
-		if expr == nil {
-			return
-		}
 		kind = dbscheme.CallOrConversionExpr.Index()
 		extractExpr(tw, expr.Fun, lbl, 0, false)
 		extractExprs(tw, expr.Args, lbl, 1, 1)
@@ -1113,22 +1086,13 @@ func extractExpr(tw *trap.Writer, expr ast.Expr, parent trap.Label, idx int, ski
 			dbscheme.HasEllipsisTable.Emit(tw, lbl)
 		}
 	case *ast.StarExpr:
-		if expr == nil {
-			return
-		}
 		kind = dbscheme.StarExpr.Index()
 		extractExpr(tw, expr.X, lbl, 0, false)
 	case *ast.KeyValueExpr:
-		if expr == nil {
-			return
-		}
 		kind = dbscheme.KeyValueExpr.Index()
 		extractExpr(tw, expr.Key, lbl, 0, false)
 		extractExpr(tw, expr.Value, lbl, 1, false)
 	case *ast.UnaryExpr:
-		if expr == nil {
-			return
-		}
 		if expr.Op == token.TILDE {
 			kind = dbscheme.TypeSetLiteralExpr.Index()
 		} else {
@@ -1140,9 +1104,6 @@ func extractExpr(tw *trap.Writer, expr ast.Expr, parent trap.Label, idx int, ski
 		}
 		extractExpr(tw, expr.X, lbl, 0, false)
 	case *ast.BinaryExpr:
-		if expr == nil {
-			return
-		}
 		_, isUnionType := typeOf(tw, expr).(*types.Union)
 		if expr.Op == token.OR && isUnionType {
 			kind = dbscheme.TypeSetLiteralExpr.Index()
@@ -1158,46 +1119,28 @@ func extractExpr(tw *trap.Writer, expr ast.Expr, parent trap.Label, idx int, ski
 			extractExpr(tw, expr.Y, lbl, 1, false)
 		}
 	case *ast.ArrayType:
-		if expr == nil {
-			return
-		}
 		kind = dbscheme.ArrayTypeExpr.Index()
 		extractExpr(tw, expr.Len, lbl, 0, false)
 		extractExpr(tw, expr.Elt, lbl, 1, false)
 	case *ast.StructType:
-		if expr == nil {
-			return
-		}
 		kind = dbscheme.StructTypeExpr.Index()
 		extractFields(tw, expr.Fields, lbl, 0, 1)
 	case *ast.FuncType:
-		if expr == nil {
-			return
-		}
 		kind = dbscheme.FuncTypeExpr.Index()
 		extractFields(tw, expr.Params, lbl, 0, 1)
 		extractFields(tw, expr.Results, lbl, -1, -1)
 		emitScopeNodeInfo(tw, expr, lbl)
 	case *ast.InterfaceType:
-		if expr == nil {
-			return
-		}
 		kind = dbscheme.InterfaceTypeExpr.Index()
 		// expr.Methods contains methods, embedded interfaces and type set
 		// literals.
 		makeTypeSetLiteralsUnionTyped(tw, expr.Methods)
 		extractFields(tw, expr.Methods, lbl, 0, 1)
 	case *ast.MapType:
-		if expr == nil {
-			return
-		}
 		kind = dbscheme.MapTypeExpr.Index()
 		extractExpr(tw, expr.Key, lbl, 0, false)
 		extractExpr(tw, expr.Value, lbl, 1, false)
 	case *ast.ChanType:
-		if expr == nil {
-			return
-		}
 		tp := dbscheme.ChanTypeExprs[expr.Dir]
 		if tp == nil {
 			log.Fatalf("unsupported channel direction %v", expr.Dir)
@@ -1299,7 +1242,15 @@ func extractFields(tw *trap.Writer, fields *ast.FieldList, parent trap.Label, id
 // extractStmt extracts AST information for a given statement and all other statements or expressions
 // nested inside it
 func extractStmt(tw *trap.Writer, stmt ast.Stmt, parent trap.Label, idx int) {
-	if stmt == nil {
+	if stmt == nil || stmt == (*ast.DeclStmt)(nil) ||
+		stmt == (*ast.LabeledStmt)(nil) || stmt == (*ast.ExprStmt)(nil) ||
+		stmt == (*ast.SendStmt)(nil) || stmt == (*ast.IncDecStmt)(nil) ||
+		stmt == (*ast.AssignStmt)(nil) || stmt == (*ast.GoStmt)(nil) ||
+		stmt == (*ast.DeferStmt)(nil) || stmt == (*ast.BranchStmt)(nil) ||
+		stmt == (*ast.BlockStmt)(nil) || stmt == (*ast.IfStmt)(nil) ||
+		stmt == (*ast.CaseClause)(nil) || stmt == (*ast.SwitchStmt)(nil) ||
+		stmt == (*ast.TypeSwitchStmt)(nil) || stmt == (*ast.CommClause)(nil) ||
+		stmt == (*ast.ForStmt)(nil) || stmt == (*ast.RangeStmt)(nil) {
 		return
 	}
 
@@ -1309,37 +1260,22 @@ func extractStmt(tw *trap.Writer, stmt ast.Stmt, parent trap.Label, idx int) {
 	case *ast.BadStmt:
 		kind = dbscheme.BadStmtType.Index()
 	case *ast.DeclStmt:
-		if stmt == nil {
-			return
-		}
 		kind = dbscheme.DeclStmtType.Index()
 		extractDecl(tw, stmt.Decl, lbl, 0)
 	case *ast.EmptyStmt:
 		kind = dbscheme.EmptyStmtType.Index()
 	case *ast.LabeledStmt:
-		if stmt == nil {
-			return
-		}
 		kind = dbscheme.LabeledStmtType.Index()
 		extractExpr(tw, stmt.Label, lbl, 0, false)
 		extractStmt(tw, stmt.Stmt, lbl, 1)
 	case *ast.ExprStmt:
-		if stmt == nil {
-			return
-		}
 		kind = dbscheme.ExprStmtType.Index()
 		extractExpr(tw, stmt.X, lbl, 0, false)
 	case *ast.SendStmt:
-		if stmt == nil {
-			return
-		}
 		kind = dbscheme.SendStmtType.Index()
 		extractExpr(tw, stmt.Chan, lbl, 0, false)
 		extractExpr(tw, stmt.Value, lbl, 1, false)
 	case *ast.IncDecStmt:
-		if stmt == nil {
-			return
-		}
 		if stmt.Tok == token.INC {
 			kind = dbscheme.IncStmtType.Index()
 		} else if stmt.Tok == token.DEC {
@@ -1349,9 +1285,6 @@ func extractStmt(tw *trap.Writer, stmt ast.Stmt, parent trap.Label, idx int) {
 		}
 		extractExpr(tw, stmt.X, lbl, 0, false)
 	case *ast.AssignStmt:
-		if stmt == nil {
-			return
-		}
 		tp := dbscheme.AssignStmtTypes[stmt.Tok]
 		if tp == nil {
 			log.Fatalf("unsupported assignment statement with operator %v", stmt.Tok)
@@ -1360,24 +1293,15 @@ func extractStmt(tw *trap.Writer, stmt ast.Stmt, parent trap.Label, idx int) {
 		extractExprs(tw, stmt.Lhs, lbl, -1, -1)
 		extractExprs(tw, stmt.Rhs, lbl, 1, 1)
 	case *ast.GoStmt:
-		if stmt == nil {
-			return
-		}
 		kind = dbscheme.GoStmtType.Index()
 		extractExpr(tw, stmt.Call, lbl, 0, false)
 	case *ast.DeferStmt:
-		if stmt == nil {
-			return
-		}
 		kind = dbscheme.DeferStmtType.Index()
 		extractExpr(tw, stmt.Call, lbl, 0, false)
 	case *ast.ReturnStmt:
 		kind = dbscheme.ReturnStmtType.Index()
 		extractExprs(tw, stmt.Results, lbl, 0, 1)
 	case *ast.BranchStmt:
-		if stmt == nil {
-			return
-		}
 		switch stmt.Tok {
 		case token.BREAK:
 			kind = dbscheme.BreakStmtType.Index()
@@ -1392,16 +1316,10 @@ func extractStmt(tw *trap.Writer, stmt ast.Stmt, parent trap.Label, idx int) {
 		}
 		extractExpr(tw, stmt.Label, lbl, 0, false)
 	case *ast.BlockStmt:
-		if stmt == nil {
-			return
-		}
 		kind = dbscheme.BlockStmtType.Index()
 		extractStmts(tw, stmt.List, lbl, 0, 1)
 		emitScopeNodeInfo(tw, stmt, lbl)
 	case *ast.IfStmt:
-		if stmt == nil {
-			return
-		}
 		kind = dbscheme.IfStmtType.Index()
 		extractStmt(tw, stmt.Init, lbl, 0)
 		extractExpr(tw, stmt.Cond, lbl, 1, false)
@@ -1409,35 +1327,23 @@ func extractStmt(tw *trap.Writer, stmt ast.Stmt, parent trap.Label, idx int) {
 		extractStmt(tw, stmt.Else, lbl, 3)
 		emitScopeNodeInfo(tw, stmt, lbl)
 	case *ast.CaseClause:
-		if stmt == nil {
-			return
-		}
 		kind = dbscheme.CaseClauseType.Index()
 		extractExprs(tw, stmt.List, lbl, -1, -1)
 		extractStmts(tw, stmt.Body, lbl, 0, 1)
 		emitScopeNodeInfo(tw, stmt, lbl)
 	case *ast.SwitchStmt:
-		if stmt == nil {
-			return
-		}
 		kind = dbscheme.ExprSwitchStmtType.Index()
 		extractStmt(tw, stmt.Init, lbl, 0)
 		extractExpr(tw, stmt.Tag, lbl, 1, false)
 		extractStmt(tw, stmt.Body, lbl, 2)
 		emitScopeNodeInfo(tw, stmt, lbl)
 	case *ast.TypeSwitchStmt:
-		if stmt == nil {
-			return
-		}
 		kind = dbscheme.TypeSwitchStmtType.Index()
 		extractStmt(tw, stmt.Init, lbl, 0)
 		extractStmt(tw, stmt.Assign, lbl, 1)
 		extractStmt(tw, stmt.Body, lbl, 2)
 		emitScopeNodeInfo(tw, stmt, lbl)
 	case *ast.CommClause:
-		if stmt == nil {
-			return
-		}
 		kind = dbscheme.CommClauseType.Index()
 		extractStmt(tw, stmt.Comm, lbl, 0)
 		extractStmts(tw, stmt.Body, lbl, 1, 1)
@@ -1446,9 +1352,6 @@ func extractStmt(tw *trap.Writer, stmt ast.Stmt, parent trap.Label, idx int) {
 		kind = dbscheme.SelectStmtType.Index()
 		extractStmt(tw, stmt.Body, lbl, 0)
 	case *ast.ForStmt:
-		if stmt == nil {
-			return
-		}
 		kind = dbscheme.ForStmtType.Index()
 		extractStmt(tw, stmt.Init, lbl, 0)
 		extractExpr(tw, stmt.Cond, lbl, 1, false)
@@ -1456,9 +1359,6 @@ func extractStmt(tw *trap.Writer, stmt ast.Stmt, parent trap.Label, idx int) {
 		extractStmt(tw, stmt.Body, lbl, 3)
 		emitScopeNodeInfo(tw, stmt, lbl)
 	case *ast.RangeStmt:
-		if stmt == nil {
-			return
-		}
 		kind = dbscheme.RangeStmtType.Index()
 		extractExpr(tw, stmt.Key, lbl, 0, false)
 		extractExpr(tw, stmt.Value, lbl, 1, false)
@@ -1486,15 +1386,15 @@ func extractStmts(tw *trap.Writer, stmts []ast.Stmt, parent trap.Label, idx int,
 
 // extractDecl extracts AST information for the given declaration
 func extractDecl(tw *trap.Writer, decl ast.Decl, parent trap.Label, idx int) {
+	if decl == (*ast.FuncDecl)(nil) || decl == (*ast.GenDecl)(nil) {
+		return
+	}
 	lbl := tw.Labeler.LocalID(decl)
 	var kind int
 	switch decl := decl.(type) {
 	case *ast.BadDecl:
 		kind = dbscheme.BadDeclType.Index()
 	case *ast.GenDecl:
-		if decl == nil {
-			return
-		}
 		switch decl.Tok {
 		case token.IMPORT:
 			kind = dbscheme.ImportDeclType.Index()
@@ -1512,9 +1412,6 @@ func extractDecl(tw *trap.Writer, decl ast.Decl, parent trap.Label, idx int) {
 		}
 		extractDoc(tw, decl.Doc, lbl)
 	case *ast.FuncDecl:
-		if decl == nil {
-			return
-		}
 		kind = dbscheme.FuncDeclType.Index()
 		extractFields(tw, decl.Recv, lbl, -1, -1)
 		extractExpr(tw, decl.Name, lbl, 0, false)