input: Write a function to generate an array of random numbers using Python's NumPy library. The function should take an integer 'size' as input and return an array of that size filled with random integers between 0 and 99. If 'size' is not provided, the function should default to generating an array of size 10. If 'size' is negative, the function should return an empty array.
  
  def generate_random_array(size=10):
      if size < 0:
          return []
      return np.random.randint(0, 100, size)
  
  import numpy as np
  
  assert len(generate_random_array(5)) == 5
  assert len(generate_random_array(10)) == 10
  assert len(generate_random_array(-1)) == 0
  assert len(generate_random_array()) == 10
output: def generate_random_array(size=10):
      if size < 0:
          return []
      return np.random.randint(0, 100, size)