code: def safe_max_abs_diff(A, ia, B, ib):
      """Compute np.max(np.abs(A)) possible with empty A."""
      A = A[ia] if np.sum(ia) else 0.0
      B = B[ib] if np.sum(ia) else 0.0
      return np.max(np.abs(A - B))
  
imports: import functools
  from math import sqrt
  import numpy
  from ..time_frequency._stft import istft, stft, stft_norm1, stft_norm2
  from ..utils import _check_option, _get_blas_funcs, _validate_type, logger, sum_squared, verbose, warn
  from .mxne_debiasing import compute_bias
label_desc: Use image node_id 14 for calling a global function with example usage: safe_max_abs_diff(A, ia, B, ib) and returns: np