input: Write a python function named 'pluck' that takes in a list of non-negative integers representing nodes on a branch of a tree. The function should return the node with the smallest even value and its index in a list format [smallest_value, index]. If there are multiple nodes with the smallest even value, return the one with the smallest index. If no even values are present or if the list is empty, return an empty list.
  
  Example 1:
      Input: [4,2,3]
      Output: [2, 1]
      Explanation: 2 is the smallest even value and has the smallest index.
  
  Example 2:
      Input: [1,2,3]
      Output: [2, 1]
      Explanation: 2 is the smallest even value and has the smallest index.
  
  Example 3:
      Input: []
      Output: []
  
  Example 4:
      Input: [5, 0, 3, 0, 4, 2]
      Output: [0, 1]
      Explanation: 0 is the smallest value but there are two zeros, so return the first zero with the smallest index.
  
  Constraints:
      * 1 <= nodes.length <= 10000
      * 0 <= node.value
output: def pluck(nodes):
      smallest_even = float('inf')
      index_of_smallest = -1
      for index, value in enumerate(nodes):
          if value % 2 == 0 and value < smallest_even:
              smallest_even = value
              index_of_smallest = index
      if smallest_even == float('inf'):
          return []
      return [smallest_even, index_of_smallest]