From 1da6d9ae4ec9abbf2f1bed3ea0b4ef78a6902ee8 Mon Sep 17 00:00:00 2001
From: Christopher Mayes <31023527+ChristopherMayes@users.noreply.github.com>
Date: Wed, 28 Jun 2023 11:34:21 -0700
Subject: [PATCH] Fix bug where z=0 or t=0 drift was actually setting to the
 mean.

---
 pmd_beamphysics/particles.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pmd_beamphysics/particles.py b/pmd_beamphysics/particles.py
index 5e95acb..dae4ac5 100644
--- a/pmd_beamphysics/particles.py
+++ b/pmd_beamphysics/particles.py
@@ -738,7 +738,7 @@ def drift(self, delta_t):
     
     def drift_to_z(self, z=None):
 
-        if not z:
+        if z is None:
             z = self.avg('z')
         dt = (z - self.z) / (self.beta_z * c_light)
         self.drift(dt)
@@ -752,7 +752,7 @@ def drift_to_t(self, t=None):
         
         If no z is given, particles will be drifted to the average t
         """
-        if not t:
+        if t is None:
             t = self.avg('t')
         dt = t - self.t
         self.drift(dt)