GP-5459: For userop libraries, treat empty as empty, not unimpl

Ghidra/Features/SystemEmulation/src/test/java/ghidra/pcode/struct/sub/StructuredSleighTest.java

@@ -4,9 +4,9 @@
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
- * 
+ *
  *      http://www.apache.org/licenses/LICENSE-2.0
- * 
+ *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -16,6 +16,7 @@
 package ghidra.pcode.struct.sub;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
 
 import java.lang.invoke.MethodHandles;
 import java.lang.invoke.MethodHandles.Lookup;
@@ -25,8 +26,7 @@ import org.junit.Before;
 import org.junit.Test;
 
 import ghidra.app.plugin.processors.sleigh.SleighException;
-import ghidra.pcode.exec.PcodeUseropLibrary;
-import ghidra.pcode.exec.SleighPcodeUseropDefinition;
+import ghidra.pcode.exec.*;
 import ghidra.pcode.struct.StructuredSleigh;
 import ghidra.program.model.lang.*;
 import ghidra.program.model.pcode.Varnode;
@@ -238,4 +238,16 @@ public class StructuredSleighTest extends AbstractGhidraHeadlessIntegrationTest
 		// TODO: Test that the generated code compiles in a slaspec file.
 		// It's rejected for injects because "return" is not valid there.
 	}
+
+	@Test
+	public void testEmpty() throws Exception {
+		StructuredSleigh ss = new TestStructuredSleigh() {
+			@StructuredUserop
+			public void my_userop() {
+			}
+		};
+		SleighPcodeUseropDefinition<Object> myUserop = ss.generate().get("my_userop");
+		PcodeProgram program = myUserop.programFor(null, List.of(), PcodeUseropLibrary.nil());
+		assertTrue(program.getCode().isEmpty());
+	}
 }