You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: logical.go
    path of file: ./repos/octosql/logical
    
    the code of the file until where you have to start completion: package logical

import (
	"context"
	"fmt"
	"strings"
	"time"

	"github.com/cube2222/octosql/execution"
	"github.com/cube2222/octosql/octosql"
	"github.com/cube2222/octosql/physical"
)

type Environment struct {
	CommonTableExpressions map[string]CommonTableExpression
	TableValuedFunctions   map[string]TableValuedFunctionDescription
	UniqueVariableNames    *VariableMapping
	UniqueNameGenerator    map[string]int
}

func (env *Environment) GetUnique(name string) string {
	index := env.UniqueNameGenerator[name]
	env.UniqueNameGenerator[name] = index + 1
	return fmt.Sprintf("%s_%d", name, index)
}

type CommonTableExpression struct {
	Node                  physical.Node
	UniqueVariableMapping map[string]string
}

func (env *Environment) WithRecordUniqueVariableNames(record map[string]string) Environment {
	return Environment{
		CommonTableExpressions: env.CommonTableExpressions,
		TableValuedFunctions:   env.TableValuedFunctions,
		UniqueVariableNames:    env.UniqueVariableNames.WithRecordMapping(record),
		Unique
    
func TypecheckPossiblyNullableStruct(ctx context.Context, env physical.Environment, logicalEnv Environment, expression Expression) physical.Expression {
	expr := expression.Typecheck(ctx, env, logicalEnv)
	nonNullableExprType := octosql.NonNullable(expr.Type)

	if nonNullableExprType.TypeID == octosql.TypeIDStruct {
		return expr
	}
	if nonNullableExprType.TypeID != octosql.TypeIDUnion {
		panic(fmt.Errorf("expected object or union containing object, got %s", expr.Type))
	}
	foundIndex := -1
	for i := range nonNullableExprType.Union.Alternatives {
		if nonNullableExprType.Union.Alternatives[i].TypeID == octosql.TypeIDStruct {
			foundIndex = i
			break
		}
	}
	if foundIndex == -1 {
		panic(fmt.Errorf("expected object or union containing object, got %s", expr.Type))
	}
	targetType := octosql.Type{
		TypeID: octosql.TypeIDUnion,
		Union: struct{ Alternatives []octosql.Type }{Alternatives: []octosql.Type{
			nonNullableExprType.Union.Alternatives[foundIndex],
			octosql.Null,
		}},
	}
	return physical.Expression{
		Type:           targetType,
		ExpressionType: physical.ExpressionTypeTypeAssertion,
		TypeAssertion: &physical.TypeAssertion{
			Expression: expr,
			TargetType: targetType,
		},
	}
}