Java Models Not working

So i wanted to make a mob with a java model but it gives me this error in the console:

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Executing Gradle task: runClient
Build info: MCreator 2020.3.22116, forge-1.15.2, 64-bit, 32720 MB, Windows 10, JVM 1.8.0_252, JAVA_HOME: D:\Program Files (x86)\MCreator\jdk
> Configure project :
New Dep: net.minecraftforge:forge:1.15.2-31.2.0_mapped_snapshot_20200514-1.15.1
> Task :compileJava FAILED
D:\Program Files (x86)\MCreator\Workspaces\t3st_m0d\src\main\java\net\mcreator\tstmd\entity\NautilusEntity.java:222: error: cannot find symbol @SideOnly(Side.CLIENT) public static class ModelNautilus extends EntityModel<Entity> {
^
symbol: class SideOnly
location: class NautilusEntity
1 error
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':compileJava'.
> Compilation failed; see the compiler error output for details.
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
* Get more help at https://help.gradle.org
Deprecated Gradle features were used in this build, making it incompatible with Gradle 5.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/4.10.3/userguide/command_line_interface.html#se…
BUILD FAILED in 2s
1 actionable task: 1 executed
BUILD FAILED
Task completed in 6224 milliseconds
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Here is the Java Model and texture:

https://drive.google.com/drive/folders/1Jf_B5idJ_gBR3mdhDgNwCUjtiGvskqq…