Returning empty list not supported

[Shaikh-Ubaid]

$ cat examples/expr2.py 
from lpython import i32

def return_empty_list_of_integers() -> list[i32]:
    return []

def main0():
    x: list[i32] = return_empty_list_of_integers()
    print(len(x))

    assert len(x) == 0

main0()
$ python examples/expr2.py
0
$ lpython examples/expr2.py
Internal Compiler Error: Unhandled exception
Traceback (most recent call last):
  File "/Users/ubaid/Desktop/OpenSource/lpython/src/bin/lpython.cpp", line 1822
    err = compile_python_to_object_file(arg_file, tmp_o, runtime_library_dir,
  File "/Users/ubaid/Desktop/OpenSource/lpython/src/bin/lpython.cpp", line 783
    r1 = LCompilers::LPython::python_ast_to_asr(al, lm, *ast, diagnostics, compiler_options,
  File "/Users/ubaid/Desktop/OpenSource/lpython/src/lpython/semantics/python_ast_to_asr.cpp", line 7274
    #endif
  File "/Users/ubaid/Desktop/OpenSource/lpython/src/lpython/semantics/python_ast_to_asr.cpp", line 7227
    {
  File "/Users/ubaid/Desktop/OpenSource/lpython/src/lpython/semantics/python_ast_to_asr.cpp", line 4405
    visit_stmt(*x.m_body[i]);
  File "/Users/ubaid/Desktop/OpenSource/lpython/src/lpython/python_ast.h", line 1883
    void visit_stmt(const stmt_t &b) { visit_stmt_t(b, self()); }
  File "/Users/ubaid/Desktop/OpenSource/lpython/src/lpython/python_ast.h", line 1751
    case stmtType::FunctionDef: { v.visit_FunctionDef((const FunctionDef_t &)x); return; }
  File "/Users/ubaid/Desktop/OpenSource/lpython/src/lpython/semantics/python_ast_to_asr.cpp", line 4514
    handle_fn(x, *f);
  File "/Users/ubaid/Desktop/OpenSource/lpython/src/lpython/semantics/python_ast_to_asr.cpp", line 4494
    transform_stmts(body, x.n_body, x.m_body);
  File "/Users/ubaid/Desktop/OpenSource/lpython/src/lpython/semantics/python_ast_to_asr.cpp", line 4365
    this->visit_stmt(*m_body[i]);
  File "/Users/ubaid/Desktop/OpenSource/lpython/src/lpython/python_ast.h", line 1883
    void visit_stmt(const stmt_t &b) { visit_stmt_t(b, self()); }
  File "/Users/ubaid/Desktop/OpenSource/lpython/src/lpython/python_ast.h", line 1753
    case stmtType::ClassDef: { v.visit_ClassDef((const ClassDef_t &)x); return; }
  File "/Users/ubaid/Desktop/OpenSource/lpython/src/lpython/semantics/python_ast_to_asr.cpp", line 6033
    ASR::expr_t *target = ASRUtils::EXPR(return_var_ref);
  File "/Users/ubaid/Desktop/OpenSource/lpython/src/libasr/asr_utils.h", line 34
    return ASR::down_cast<ASR::expr_t>(f);
  File "/Users/ubaid/Desktop/OpenSource/lpython/src/libasr/asr.h", line 40
    LCOMPILERS_ASSERT(f != nullptr);
AssertFailed: f != nullptr