chore: address Value field issue for empty strings in dataflow analysis

[behnazh-w]

Summary

This patch addresses an issue in the dataflow analysis related to parsing single-quoted strings in bash scripts. Previously, for empty single-quoted strings the code incorrectly assumed that a Value field with an empty string would always be present.

Description of changes

• Updated the logic to handle cases where the Value field is absent, returning an empty string when appropriate.
• Corrected the typo in function naming: parse_sql_quoted_string is now correctly named parse_sgl_quoted_string.
• Adjusted the definition of the SglQuoted class to reflect that the Value field is not always required