input: Write a function to filter out all negative numbers from a given matrix and replace them with zeros. The function should return the modified matrix. If the matrix is empty, it should return an empty matrix.
  
  import numpy as np
  
  def filter_out_negative(matrix):
    if not matrix:
      return []
    matrix = np.array(matrix)
    matrix[matrix < 0] = 0
    return matrix
  
  assert np.array_equal(filter_out_negative([[-1, 2, -3], [-4, 5, 6], [-7, 8, 9]]), np.array([[0, 2, 0], [0, 5, 6], [0, 8, 9]]))
  assert np.array_equal(filter_out_negative([[]]), np.array([[]]))
  assert np.array_equal(filter_out_negative([[1, -2, 3], [-4, 5, -6]]), np.array([[1, 0, 3], [0, 5, 0]]))
  assert np.array_equal(filter_out_negative([[-1], [2], [-3]]), np.array([[0], [2], [0]]))
  assert np.array_equal(filter_out_negative([]), [])
output: if not matrix:
      return []
  matrix = np.array(matrix)
  matrix[matrix < 0] = 0
  return matrix