System: As an API testing assistant, analyze API specifications and previous test results to generate new, unused parameters. Avoid using any parameters from the previous attempts. Return only the parameter dictionary.
User: API Specification:
URL: https://gaialens-historical-esg-scores.p.rapidapi.com/scores/historical/{year}
Method: GET
Required Parameters: [{'name': 'year', 'type': 'string', 'description': 'The year for which historical scores are requested. Must be less than or equal to 2020.', 'default': '2020'}]
Optional Parameters: [{'name': 'Content-Type', 'type': 'string', 'description': 'Specifies the media type of the resource.', 'default': ''}, {'name': 'sedol', 'type': 'string', 'description': 'The SEDOL code for the company.', 'default': ''}, {'name': 'isin', 'type': 'string', 'description': 'The ISIN code for the company.', 'default': ''}, {'name': 'companyname', 'type': 'string', 'description': 'The name of the company for which scores are requested.', 'default': 'Apple Inc.'}]
Previous attempts: Initial Attempt 1:
Parameters: {'year': '2019', 'Content-Type': 'application/json', 'sedol': 'B1Y8QZ3', 'isin': 'US0378331005', 'companyname': 'Microsoft Corp'}
Result: Failed
Analysis: Failed - possible issues: Message from API: Bad request syntax or unsupported method - invalid request parameter(s)

Initial Attempt 2:
Parameters: {'year': '2020', 'Content-Type': 'application/json', 'sedol': 'B1Y8QZ4', 'isin': 'US02079K3059', 'companyname': 'Tesla Inc.'}
Result: Failed
Analysis: Failed - possible issues: Message from API: Bad request syntax or unsupported method - invalid request parameter(s)

Recent Attempt 3:
Parameters: {'year': '2020', 'Content-Type': 'text/plain', 'sedol': 'B1Y8QZ6', 'isin': 'US02079K3067', 'companyname': 'Amazon.com Inc.'}
Result: Failed
Analysis: Failed - possible issues: Message from API: Bad request syntax or unsupported method - invalid request parameter(s)

Recent Attempt 4:
Parameters: {'year': '2018', 'Content-Type': 'application/vnd.api+json', 'sedol': 'B1Y8QZ7', 'isin': 'US0378331007', 'companyname': 'Netflix Inc.'}
Result: Failed
Analysis: Failed - possible issues: Message from API: Bad request syntax or unsupported method - invalid request parameter(s)

Recent Attempt 5:
Parameters: {'year': '2020', 'Content-Type': 'application/json', 'sedol': 'B1Y8QZ8', 'isin': 'US02079K3075', 'companyname': 'Facebook Inc.'}
Result: Failed
Analysis: Failed - possible issues: Message from API: Bad request syntax or unsupported method - invalid request parameter(s)

Already used parameters: - {'Content-Type': 'application/json', 'companyname': 'Microsoft Corp', 'isin': 'US0378331005', 'sedol': 'B1Y8QZ3', 'year': '2019'}
- {'Content-Type': 'application/xml', 'companyname': 'Google LLC', 'isin': 'US0378331006', 'sedol': 'B1Y8QZ5', 'year': '2020'}
- {'Content-Type': 'application/json', 'companyname': 'Facebook Inc.', 'isin': 'US02079K3075', 'sedol': 'B1Y8QZ8', 'year': '2020'}
- {'Content-Type': 'text/plain', 'companyname': 'Amazon.com Inc.', 'isin': 'US02079K3067', 'sedol': 'B1Y8QZ6', 'year': '2020'}
- {'Content-Type': 'application/vnd.api+json', 'companyname': 'Netflix Inc.', 'isin': 'US0378331007', 'sedol': 'B1Y8QZ7', 'year': '2018'}
- {'Content-Type': 'application/json', 'companyname': 'Tesla Inc.', 'isin': 'US02079K3059', 'sedol': 'B1Y8QZ4', 'year': '2020'}

Rules:
1. If required_parameters is empty and you choose not to use optional parameters, return empty dict.
2. If using optional parameters, only use parameters exactly as defined in optional_parameters.
3. Do not create new parameters that are not in the specification.

Generate valid parameters:
Assistant: