[wpimath] Trajectory: Throw on empty lists of States (#5497)

Fixes #4141.

wpimath/src/main/java/edu/wpi/first/math/trajectory/Trajectory.java

@@ -30,9 +30,15 @@ public class Trajectory {
    * Constructs a trajectory from a vector of states.
    *
    * @param states A vector of states.
+   * @throws IllegalArgumentException if the vector of states is empty.
    */
   public Trajectory(final List<State> states) {
     m_states = states;
+
+    if (m_states.isEmpty()) {
+      throw new IllegalArgumentException("Trajectory manually created with no states.");
+    }
+
     m_totalTimeSeconds = m_states.get(m_states.size() - 1).timeSeconds;
   }
 
@@ -92,8 +98,13 @@ public class Trajectory {
    *
    * @param timeSeconds The point in time since the beginning of the trajectory to sample.
    * @return The state at that point in time.
+   * @throws IllegalStateException if the trajectory has no states.
    */
   public State sample(double timeSeconds) {
+    if (m_states.isEmpty()) {
+      throw new IllegalStateException("Trajectory cannot be sampled if it has no states.");
+    }
+
     if (timeSeconds <= m_states.get(0).timeSeconds) {
       return m_states.get(0);
     }

wpimath/src/main/native/cpp/trajectory/Trajectory.cpp

@@ -5,6 +5,7 @@
 #include "frc/trajectory/Trajectory.h"
 
 #include <algorithm>
+#include <stdexcept>
 
 #include <wpi/MathExtras.h>
 #include <wpi/json.h>
@@ -54,10 +55,20 @@ Trajectory::State Trajectory::State::Interpolate(State endValue,
 }
 
 Trajectory::Trajectory(const std::vector<State>& states) : m_states(states) {
+  if (m_states.empty()) {
+    throw std::invalid_argument(
+        "Trajectory manually initialized with no states.");
+  }
+
   m_totalTime = states.back().t;
 }
 
 Trajectory::State Trajectory::Sample(units::second_t t) const {
+  if (m_states.empty()) {
+    throw std::runtime_error(
+        "Trajectory cannot be sampled if it has no states.");
+  }
+
   if (t <= m_states.front().t) {
     return m_states.front();
   }

wpimath/src/main/native/include/frc/trajectory/Trajectory.h

@@ -66,6 +66,8 @@ class WPILIB_DLLEXPORT Trajectory {
 
   /**
    * Constructs a trajectory from a vector of states.
+   *
+   * @throws std::invalid_argument if the vector of states is empty.
    */
   explicit Trajectory(const std::vector<State>& states);
 
@@ -77,6 +79,7 @@ class WPILIB_DLLEXPORT Trajectory {
 
   /**
    * Return the states of the trajectory.
+   *
    * @return The states of the trajectory.
    */
   const std::vector<State>& States() const { return m_states; }
@@ -86,6 +89,7 @@ class WPILIB_DLLEXPORT Trajectory {
    *
    * @param t The point in time since the beginning of the trajectory to sample.
    * @return The state at that point in time.
+   * @throws std::runtime_error if the trajectory has no states.
    */
   State Sample(units::second_t t) const;