add check for empty command_str in _search_in_extension_commands (#17047)
add check for empty command_str in _search_in_extension_commands (#17047)


yugangw-msft/azure-cli,yugangw-msft/azure-cli,yugangw-msft/azure-cli,yugangw-msft/azure-cli,yugangw-msft/azure-cli,yugangw-msft/azure-cli