Optional closing tag causes runtime error: Earley generates multiple start symbol items

[caph1993]

Describe the bug

I defined the following grammar with ambiguity enabled. The parser raised and error and automatically suggested me to report the bug.

Note. The example below is a minimal example of my real use case.

To Reproduce

# Bug report
from lark import Lark, UnexpectedCharacters

grammar = """
    start: "<p>" text ("<b>" bold "</b>")* CLOSE?
    text:  /.+/
    bold: /.+/
    CLOSE: "</p>"
    %ignore CLOSE
    
    %import common.WS
"""

# Use ambiguity='explicit' to see all possible trees
parser = Lark(grammar, start='start', ambiguity='explicit', lexer='dynamic_complete')

text = "<p>Press the <b>button</b>.</p>"
print(text)
try:
    print(parser.parse(text).pretty())
except UnexpectedCharacters:
    print("No matches")

Output:

RuntimeError: Earley should not generate multiple start symbol items! Please report this bug.

[erezsh]

We just recently had a fix related to this error. Can you try using the master branch?