Nested File System Builder

You are given a list of strings where each string represents a file path in a file system. The file paths use the forward slash / as the directory separator. Write a function that builds a nested data structure (e.g., a dictionary in Python or an object in JavaScript) representing the file system hierarchy.

For example, given the following input:

[
  "folder1/file1.txt",
  "folder1/folder2/file2.txt",
  "folder3/file3.pdf"
]

Your function should return a nested structure similar to:

{
  "folder1": {
    "file1.txt": null,
    "folder2": {
      "file2.txt": null
    }
  },
  "folder3": {
    "file3.pdf": null
  }
}

Notes:

• Every component in a path that is not the last element is considered a directory. The last element is considered a file.
• You can assume that the input does not include explicit entries for directories (i.e., directories are only present as part of a file path).
• The output structure should reflect the hierarchy of directories and files.

Implement your solution in the programming language of your choice.