Lark IndexError

"""
IndexError_ChildFilterLALR_NoPlaceholders_2020-11.py

https://github.com/lark-parser/lark/issues/754

Works in Lark 0.9, but not 0.10.1 or github master on 2020-11-12
Python 3.8.5 64-bit on Win 10 Pro

python IndexError_ChildFilterLALR_NoPlaceholders_2020-11.py

Expected output is:
    code: ...
    parser: ...
    tree: ...
    Done.

Works on Lark 0.9.0
On Lark 0.10.1 or latest master branch, raises IndexError:

Traceback (most recent call last):
  File "IndexError_ChildFilterLALR_NoPlaceholders_2020-11.py", line 104, in <module>
    tree = p.parse(code)
  File "...\lark-github\lark\lark.py", line 494, in parse
    return self.parser.parse(text, start=start)
  File "...\lark-github\lark\parser_frontends.py", line 138, in parse
    return self._parse(start, self.make_lexer(text))
  File "...\lark-github\lark\parser_frontends.py", line 73, in _parse
    return self.parser.parse(input, start, *args)
  File "...\lark-github\lark\parsers\earley.py", line 320, in parse
    return transformer.transform(solutions[0])
  File "...\lark-github\lark\parsers\earley_forest.py", line 353, in transform
    self.visit(root)
  File "...\lark-github\lark\parsers\earley_forest.py", line 295, in visit
    vpno(current)
  File "...\lark-github\lark\parsers\earley_forest.py", line 587, in visit_packed_node_out
    super(ForestToParseTree, self).visit_packed_node_out(node)
  File "...\lark-github\lark\parsers\earley_forest.py", line 417, in visit_packed_node_out
    transformed = self.transform_packed_node(node, self.data[id(node)])
  File "...\lark-github\lark\parsers\earley_forest.py", line 570, in transform_packed_node
    return self._call_rule_func(node, children)
  File "...\lark-github\lark\parsers\earley_forest.py", line 524, in _call_rule_func
    return self.callbacks[node.rule](data)
  File "...\lark-github\lark\parse_tree_builder.py", line 29, in __call__
    res = self.node_builder(children)
  File "...\lark-github\lark\parse_tree_builder.py", line 129, in __call__
    filtered.append(children[i])
IndexError: list index out of range
"""
import lark
import lark.indenter
code = '''\
if a is b
    print(a)
'''
# improper subset of one of the Python grammar examples:
grammar = r"""
file_input: (_NEWLINE | stmt)*

?stmt: simple_stmt | compound_stmt
?simple_stmt: small_stmt (";" small_stmt)* [";"] _NEWLINE
?small_stmt: (NAME test)

?compound_stmt: if_stmt
if_stmt: "if" test ":"? suite
suite: (","? simple_stmt) | (_NEWLINE _INDENT stmt+ _DEDENT)

?test: binary_bool_test
?binary_bool_test: not_test (("and" | "or") not_test)*
?not_test: "not" not_test -> not | comparison
?comparison: expr (_comp_op expr)*
star_expr: "*" expr
?expr: shift_expr (("bor" | "band" | "bxor") shift_expr)*
?shift_expr: arith_expr (_shift_op arith_expr)*
?arith_expr: term (_add_op term)*
?term: factor (_mul_op factor)*
?factor: _factor_op factor | atom_expr

_factor_op: "+" | "-"
_add_op:    "+" | "-"
_shift_op:  "<<" | ">>"
_mul_op:    "*" | "/" | "%" | "//"
_comp_op:   "<" | ">" | "==" | ">=" | "<=" | "<>" | "in" | "is"

?atom_expr: atom_expr "(" [arguments] ")" -> func_call
          | atom

?atom: "(" test ")"
     | name
     | number

name: NAME
?number: INT_LITERAL_DEC

?testlist_comp: (test|star_expr) [("," (test|star_expr))+ [","] | ","]
exprlist: (expr|star_expr) ("," (expr|star_expr))* [","]
testlist: test ("," test)* [","]

arguments: argvalue ("," argvalue)*  ("," [starargs | kwargs])?
         | starargs
         | kwargs

starargs: "*" test ("," "*" test)* ("," argvalue)* ["," kwargs]
kwargs: "**" test

?argvalue: test ("=" test)?

NAME: /[a-zA-Z_]\w*/
_NEWLINE: ( /\r?\n[\t ]*/  )+
INT_LITERAL_DEC:   /0|[1-9]\d*/i

%ignore /[\t \f]+/  // WS
%ignore /\\[\t \f]*\r?\n/   // LINE_CONT
%declare _INDENT _DEDENT
"""

# for Pythonic indentation:
class CustomIndenter(lark.indenter.Indenter):
    NL_type = '_NEWLINE'
    OPEN_PAREN_types = ['LPAR', 'LSQB', 'LBRACE']
    CLOSE_PAREN_types = ['RPAR', 'RSQB', 'RBRACE']
    INDENT_type = '_INDENT'
    DEDENT_type = '_DEDENT'
    tab_len = 8

def parser():
    return lark.Lark(
        grammar,
        debug=True,
        parser='earley',      # lalr, earley
        lexer='standard',     # in ('standard', 'contextual', 'dynamic', 'dynamic_complete') or issubclass(lexer, Lexer)
        postlex=CustomIndenter(),
        start='file_input',
        keep_all_tokens=True,
        maybe_placeholders=True,
        propagate_positions=True,
        ambiguity='resolve')  # in ('resolve', 'explicit', 'auto')

print('code:')
print(code)

p = parser()
print('parser:', p)
tree = p.parse(code)
print('tree:', tree)

print('Done.')