cleanup(generator): remove javax.annotation.Nonnull usage (#13960)

This PR removes all occurrences of `javax.annotation.Nonnull` (both
imports and annotations) from the codebase of `gapic-generator-java`.

### Why this change is needed:
As part of the migration to JSpecify annotations, generator classes are
annotated with `@NullMarked`, making all unannotated types non-nullable
by default. The legacy `javax.annotation.Nonnull` annotations are
redundant and can be safely removed.

### Changes:
- Removed `import javax.annotation.Nonnull;` and `@Nonnull` from 4 files
in the generator codebase (`TypeParser.java`,
`SourceCodeInfoLocation.java`, `TryCatchStatement.java`, and
`ImportWriterVisitor.java`).
- Formatted the modified files using `fmt-maven-plugin`.
- Verified that all compilation references to `javax.annotation.Nonnull`
under `gapic-generator-java` have been eliminated.

Author: nnicolee

sdk-platform-java/gapic-generator-java/pom.xml

@@ -398,11 +398,7 @@
       <version>${junit.version}</version>
       <scope>test</scope>
     </dependency>
-    <dependency>
-      <groupId>com.google.code.findbugs</groupId>
-      <artifactId>jsr305</artifactId>
-      <version>3.0.2</version>
-    </dependency>
+
     <dependency>
       <groupId>com.google.api</groupId>
       <artifactId>api-common</artifactId>

sdk-platform-java/gapic-generator-java/src/main/java/com/google/api/generator/engine/ast/TryCatchStatement.java

@@ -20,7 +20,6 @@
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
-import javax.annotation.Nonnull;
 import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 
@@ -62,7 +61,7 @@ public abstract static class Builder {
 
     public abstract Builder setIsSampleCode(boolean isSampleCode);
 
-    public Builder addCatch(@Nonnull VariableExpr variableExpr, List<Statement> body) {
+    public Builder addCatch(VariableExpr variableExpr, List<Statement> body) {
       List<VariableExpr> catchVarExprs = new ArrayList<>(catchVariableExprs());
       catchVarExprs.add(variableExpr);
       setCatchVariableExprs(catchVarExprs);

sdk-platform-java/gapic-generator-java/src/main/java/com/google/api/generator/engine/writer/ImportWriterVisitor.java

@@ -69,7 +69,6 @@
 import java.util.Set;
 import java.util.TreeSet;
 import java.util.stream.Collectors;
-import javax.annotation.Nonnull;
 import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 
@@ -93,12 +92,12 @@ public void clear() {
     importShortNames.clear();
   }
 
-  public void initialize(@Nonnull String currentPackage) {
+  public void initialize(String currentPackage) {
     this.currentPackage = currentPackage;
     currentClassName = null;
   }
 
-  public void initialize(@Nonnull String currentPackage, @Nonnull String currentClassName) {
+  public void initialize(String currentPackage, String currentClassName) {
     this.currentPackage = currentPackage;
     this.currentClassName = currentClassName;
   }

sdk-platform-java/gapic-generator-java/src/main/java/com/google/api/generator/gapic/model/SourceCodeInfoLocation.java

@@ -15,7 +15,6 @@
 package com.google.api.generator.gapic.model;
 
 import com.google.protobuf.DescriptorProtos.SourceCodeInfo.Location;
-import javax.annotation.Nonnull;
 import org.jspecify.annotations.NullMarked;
 
 /**
@@ -24,13 +23,13 @@
  */
 @NullMarked
 public class SourceCodeInfoLocation {
-  @Nonnull private final Location location;
+  private final Location location;
 
   private SourceCodeInfoLocation(Location location) {
     this.location = location;
   }
 
-  public static SourceCodeInfoLocation create(@Nonnull Location location) {
+  public static SourceCodeInfoLocation create(Location location) {
     return new SourceCodeInfoLocation(location);
   }
 

sdk-platform-java/gapic-generator-java/src/main/java/com/google/api/generator/gapic/protoparser/TypeParser.java

@@ -34,7 +34,6 @@
 import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
-import javax.annotation.Nonnull;
 import org.jspecify.annotations.NullMarked;
 
 @NullMarked
@@ -64,7 +63,7 @@ public class TypeParser {
           .put(JavaType.BYTE_STRING, REFERENCE_BYTE_STRING)
           .build();
 
-  public static TypeNode parseType(@Nonnull FieldDescriptor field) {
+  public static TypeNode parseType(FieldDescriptor field) {
     if (field.isMapField()) {
       return createMapType(field);
     }
@@ -85,11 +84,11 @@ public static TypeNode parseType(@Nonnull FieldDescriptor field) {
     return TypeNode.withReference(parseFieldReference(field));
   }
 
-  public static TypeNode parseType(@Nonnull Descriptor messageDescriptor) {
+  public static TypeNode parseType(Descriptor messageDescriptor) {
     return TypeNode.withReference(parseMessageReference(messageDescriptor));
   }
 
-  public static TypeNode parseType(@Nonnull EnumDescriptor enumDescriptor) {
+  public static TypeNode parseType(EnumDescriptor enumDescriptor) {
     return TypeNode.withReference(parseEnumReference(enumDescriptor));
   }
 
@@ -121,7 +120,7 @@ static Reference parseFieldReference(FieldDescriptor field) {
   }
 
   @VisibleForTesting
-  static Reference parseMessageReference(@Nonnull Descriptor messageDescriptor) {
+  static Reference parseMessageReference(Descriptor messageDescriptor) {
     List<String> outerNestedTypeNames = new ArrayList<>();
     FileOptions fileOptions = messageDescriptor.getFile().getOptions();
     String javaOuterClassname =
@@ -181,7 +180,7 @@ static Reference parseMessageReference(@Nonnull Descriptor messageDescriptor) {
   }
 
   @VisibleForTesting
-  static Reference parseEnumReference(@Nonnull EnumDescriptor enumDescriptor) {
+  static Reference parseEnumReference(EnumDescriptor enumDescriptor) {
     // This is similar to parseMessageReference, but we make it a separate method because
     // EnumDescriptor and Descriptor are sibling types.
     FileOptions fileOptions = enumDescriptor.getFile().getOptions();