Codegen crash when UNIONing NULL and CHAR(N)

create table test (c1 int);
select null from test union select cast('a' as char(1)) from test;

#0  0x00007f050c4a61d7 in raise () from sysroot/lib64/libc.so.6
#1  0x00007f050c4a78c8 in abort () from sysroot/lib64/libc.so.6
#2  0x00007f050e7816b5 in os::abort(bool) ()
   from sysroot/usr/java/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so
#3  0x00007f050e91fbf3 in VMError::report_and_die() ()
   from sysroot/usr/java/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so
#4  0x00007f050e786edf in JVM_handle_linux_signal ()
   from sysroot/usr/java/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so
#5  0x00007f050e77d673 in signalHandler(int, siginfo*, void*) ()
   from sysroot/usr/java/jdk1.8.0_60/jre/lib/amd64/server/libjvm.so
#6  <signal handler called>
#7  0x0000000001a9123d in llvm::FunctionType::get(llvm::Type*, llvm::ArrayRef<llvm::Type*>, bool) ()
#8  0x0000000000c2c04f in impala::LlvmCodeGen::FnPrototype::GeneratePrototype (this=0x7f03e7fdad90,
    builder=0x0, params=0x7f03e7fdae30, print_ir=<optimized out>)
    at /usr/src/debug/impala-2.9.0-cdh5.12.2/be/src/codegen/llvm-codegen.cc:710
#9  0x0000000000846187 in impala::Expr::CreateIrFunctionPrototype (this=this@entry=0x9fded80,
    codegen=codegen@entry=0xa5a2880, name=..., args=args@entry=0x7f03e7fdae30)
    at /usr/src/debug/impala-2.9.0-cdh5.12.2/be/src/exprs/expr.cc:505
#10 0x0000000000861e5c in impala::NullLiteral::GetCodegendComputeFn (this=0x9fded80,
    codegen=0xa5a2880, fn=0x7f03e7fdaf18)
    at /usr/src/debug/impala-2.9.0-cdh5.12.2/be/src/exprs/null-literal.cc:106
#11 0x0000000000a79bc7 in impala::Tuple::CodegenMaterializeExprs (codegen=codegen@entry=0xa5a2880,
    collect_string_vals=collect_string_vals@entry=false, desc=..., materialize_expr_ctxs=...,
    use_mem_pool=use_mem_pool@entry=true, fn=0x7f03e7fdb410)
    at /usr/src/debug/impala-2.9.0-cdh5.12.2/be/src/runtime/tuple.cc:307
#12 0x0000000000d12828 in impala::UnionNode::Codegen (this=<optimized out>, state=<optimized out>)
    at /usr/src/debug/impala-2.9.0-cdh5.12.2/be/src/exec/union-node.cc:105
#13 0x0000000000c4aaa1 in impala::ExecNode::Codegen (this=this@entry=0xa0c5480,