Move set_nan_defaults from straxen to strax (#936)

strax/utils.py

@@ -124,6 +124,17 @@ def accumulate_numba_result(*args, **kwargs):
     return _growing_result
 
 
+@export
+def set_nan_defaults(buffer):
+    """When constructing the dtype, take extra care to set values to np.Nan / -1 (for ints) as 0
+    might have a meaning."""
+    for field in buffer.dtype.names:
+        if np.issubdtype(buffer.dtype[field], np.integer):
+            buffer[field][:] = -1
+        else:
+            buffer[field][:] = np.nan
+
+
 @export
 def unpack_dtype(dtype):
     """Return list of tuples needed to construct the dtype.