check for null

src/lib/src/main/java/gov/usgs/earthquake/nshmp/netcdf/Netcdf.java

@@ -38,7 +38,9 @@ public abstract class Netcdf<T> implements Comparable<Netcdf<T>> {
       throw new IllegalArgumentException("Path to Netcdf file [" + netcdfPath + "] does not exist");
     }
 
-    if (!netcdfPath.getFileName().toString().endsWith(".nc")) {
+    Path fileName = netcdfPath.getFileName();
+
+    if (fileName == null || !fileName.toString().endsWith(".nc")) {
       throw new IllegalArgumentException("NetCDF file not found (.nc) " + netcdfPath);
     }