Write a method that removes duplicate String values from a List while preserving the original order of first occurrences. The method should return a new List with unique values only.
Examples:
Input: ['apple', 'banana', 'apple', 'orange', 'banana']
Output: ['apple', 'banana', 'orange']
Explanation: Duplicates removed, first occurrence kept
Input: ['hello', 'world', 'hello']
Output: ['hello', 'world']
Explanation: Second 'hello' is removed
Input: ['a', 'b', 'c']
Output: ['a', 'b', 'c']
Explanation: No duplicates, list unchanged
Input: []
Output: []
Explanation: Empty list remains empty
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