[android] Placeholders for conversion from:to Image

platform/android/src/conversion/constant.cpp

@@ -52,6 +52,11 @@ Result<jni::Local<jni::Object<>>> Converter<jni::Local<jni::Object<>>, std::vect
     return result;
 }
 
+Result<jni::Local<jni::Object<>>> Converter<jni::Local<jni::Object<>>, style::expression::Image>::operator()(
+    jni::JNIEnv& env, const style::expression::Image& value) const {
+    return jni::Make<jni::String>(env, value.id());
+}
+
 } // namespace conversion
 } // namespace style
 } // namespace mbgl

platform/android/src/conversion/constant.hpp

@@ -6,6 +6,7 @@
 #include <mbgl/util/enum.hpp>
 
 #include <mbgl/style/expression/formatted.hpp>
+#include <mbgl/style/expression/image.hpp>
 
 #include <jni/jni.hpp>
 
@@ -99,6 +100,11 @@ struct Converter<jni::Local<jni::Object<>>, std::vector<T>, typename std::enable
     }
 };
 
+template <>
+struct Converter<jni::Local<jni::Object<>>, style::expression::Image> {
+    Result<jni::Local<jni::Object<>>> operator()(jni::JNIEnv& env, const style::expression::Image& value) const;
+};
+
 } // namespace conversion
 } // namespace android
 } // namespace mbgl