Primeira Solução,
insert into t1
select id,isnull(name,'Peter') from t2
Segunda solução
ALTER TABLE T1 ALTER COLUMN name varchar(255) NULL
insert into t1
select id,name from t2
ALTER TABLE T1 ALTER COLUMN name varchar(255) NOT NULL
insert into t1
select id,isnull(name,'Peter') from t2
ALTER TABLE T1 ALTER COLUMN name varchar(255) NULL
insert into t1
select id,name from t2
ALTER TABLE T1 ALTER COLUMN name varchar(255) NOT NULL