Fix NPE in signal ignoring logic.

Turns out the special default "null" gets turned into a null even before running the converter. Grr.

PiperOrigin-RevId: 494101769
Change-Id: Ieb1746094f53fddbbedbd18dabc1a6784973ed86

src/main/java/com/google/devtools/build/lib/dynamic/DynamicExecutionModule.java

diff --git a/src/main/java/com/google/devtools/build/lib/dynamic/DynamicExecutionModule.java b/src/main/java/com/google/devtools/build/lib/dynamic/DynamicExecutionModule.java
index 1e342c9..3e9ad8d 100644
--- a/src/main/java/com/google/devtools/build/lib/dynamic/DynamicExecutionModule.java
+++ b/src/main/java/com/google/devtools/build/lib/dynamic/DynamicExecutionModule.java
@@ -81,7 +81,9 @@
     DynamicExecutionOptions dynamicOptions =
         env.getOptions().getOptions(DynamicExecutionOptions.class);
     ignoreLocalSignals =
-        dynamicOptions != null ? dynamicOptions.ignoreLocalSignals : ImmutableSet.of();
+        dynamicOptions != null && dynamicOptions.ignoreLocalSignals != null
+            ? dynamicOptions.ignoreLocalSignals
+            : ImmutableSet.of();
     reporter = env.getReporter();
   }