Middleman actions should not have execution platforms or properties.

They only exist in order to group inputs.

PiperOrigin-RevId: 362343540

src/main/java/com/google/devtools/build/lib/actions/MiddlemanAction.java

@@ -14,9 +14,11 @@
 package com.google.devtools.build.lib.actions;
 
 import com.google.common.base.Preconditions;
+import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Iterables;
 import com.google.devtools.build.lib.actions.Artifact.ArtifactExpander;
+import com.google.devtools.build.lib.analysis.platform.PlatformInfo;
 import com.google.devtools.build.lib.cmdline.Label;
 import com.google.devtools.build.lib.collect.nestedset.NestedSet;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
@@ -96,6 +98,19 @@ public boolean mayInsensitivelyPropagateInputs() {
     return true;
   }
 
+  @Override
+  @Nullable
+  public PlatformInfo getExecutionPlatform() {
+    // Middleman actions do not execute actual actions, and therefore have no execution platform.
+    return null;
+  }
+
+  @Override
+  public ImmutableMap<String, String> getExecProperties() {
+    // Middleman actions do not execute actual actions, and therefore have no execution properties.
+    return ImmutableMap.of();
+  }
+
   /** Creates a new middleman action. */
   public static Action create(
       ActionRegistry env,