So I was playing on my city map I made and then I saw the console and found this:

[11:55:09] [Server thread/WARN]: Exception loading entity: [11:55:09] [Server thread/WARN]: Exception loading entity: s: Loading entity NBT at aom.f(SourceFile:1645) ~[1.16.1.jar:?] at aoq.a(SourceFile:468) ~[1.16.1.jar:?] at aoq$$Lambda$4134/71111758.accept(Unknown Source) ~[?:?] at v.a(SourceFile:401) ~[1.16.1.jar:?] at aoq.a(SourceFile:467) ~[1.16.1.jar:?] at aoq.b(SourceFile:530) [1.16.1.jar:?] at aoq.a(SourceFile:511) [1.16.1.jar:?] at chv.a(SourceFile:378) [1.16.1.jar:?] at chv.b(SourceFile:138) [1.16.1.jar:?] at chv$$Lambda$4047/691052308.accept(Unknown Source) [1.16.1.jar:?] at chj.w(SourceFile:479) [1.16.1.jar:?] at yp.a(SourceFile:622) [1.16.1.jar:?] at yp$$Lambda$4110/1666711156.apply(Unknown Source) [1.16.1.jar:?] at com.mojang.datafixers.util.Either.lambda$mapLeft$0(Either.java:162) [datafixerupper-3.0.25.jar:?] at com.mojang.datafixers.util.Either$$Lambda$2972/865600325.apply(Unknown Source) [datafixerupper-3.0.25.jar:?] at com.mojang.datafixers.util.Either$Left.map(Either.java:38) [datafixerupper-3.0.25.jar:?] at com.mojang.datafixers.util.Either.mapLeft(Either.java:162) [datafixerupper-3.0.25.jar:?] at yp.a(SourceFile:611) [1.16.1.jar:?] at yp$$Lambda$4107/699047167.apply(Unknown Source) [1.16.1.jar:?] at java.util.concurrent.CompletableFuture.uniApply(CompletableFuture.java:602) [?:1.8.0_51] at java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:577) [?:1.8.0_51] at java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:442) [?:1.8.0_51] at yr.b(SourceFile:58) [1.16.1.jar:?] at yr$$Lambda$4035/267684891.run(Unknown Source) [1.16.1.jar:?] at amn.c(SourceFile:144) [1.16.1.jar:?] at zb$a.c(SourceFile:545) [1.16.1.jar:?] at amn.x(SourceFile:118) [1.16.1.jar:?] at zb$a.x(SourceFile:554) [1.16.1.jar:?] at zb.d(SourceFile:280) [1.16.1.jar:?] at net.minecraft.server.MinecraftServer.aZ(SourceFile:751) [1.16.1.jar:?] at net.minecraft.server.MinecraftServer.x(SourceFile:739) [1.16.1.jar:?] at amn.c(SourceFile:127) [1.16.1.jar:?] at net.minecraft.server.MinecraftServer.w(SourceFile:724) [1.16.1.jar:?] at net.minecraft.server.MinecraftServer.v(SourceFile:676) [1.16.1.jar:?] at net.minecraft.server.MinecraftServer.a(SourceFile:256) [1.16.1.jar:?] at net.minecraft.server.MinecraftServer$$Lambda$3892/509140991.run(Unknown Source) [1.16.1.jar:?] at java.lang.Thread.run(Thread.java:745) [?:1.8.0_51]Caused by: java.lang.NullPointerException at java.util.Objects.requireNonNull(Objects.java:203) ~[?:1.8.0_51] at java.util.Optional.<init>(Optional.java:96) ~[?:1.8.0_51] at java.util.Optional.of(Optional.java:108) ~[?:1.8.0_51] at com.mojang.datafixers.util.Either$Left.left(Either.java:54) ~[datafixerupper-3.0.25.jar:?] at com.mojang.serialization.DataResult$Instance.ap3(DataResult.java:334) ~[datafixerupper-3.0.25.jar:?] at com.mojang.datafixers.Products$P3.apply(Products.java:176) ~[datafixerupper-3.0.25.jar:?] at com.mojang.datafixers.Products$P3.apply(Products.java:172) ~[datafixerupper-3.0.25.jar:?] at awl$b.a(SourceFile:75) ~[1.16.1.jar:?] at awl$$Lambda$4835/1477390246.apply(Unknown Source) ~[?:?] at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) ~[?:1.8.0_51] at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) ~[?:1.8.0_51] at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) ~[?:1.8.0_51] at java.util.Iterator.forEachRemaining(Iterator.java:116) ~[?:1.8.0_51] at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801) ~[?:1.8.0_51] at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:512) ~[?:1.8.0_51] at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:502) ~[?:1.8.0_51] at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151) ~[?:1.8.0_51] at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174) ~[?:1.8.0_51] at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[?:1.8.0_51] at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:418) ~[?:1.8.0_51] at awl.a(SourceFile:254) ~[1.16.1.jar:?] at bdp.a(SourceFile:527) ~[1.16.1.jar:?] at aom.f(SourceFile:1636) ~[1.16.1.jar:?] ... 36 more[11:55:11] [Server thread/WARN]: Exception loading entity: s: Loading entity NBT at aom.f(SourceFile:1645) ~[1.16.1.jar:?] at aoq.a(SourceFile:468) ~[1.16.1.jar:?] at aoq$$Lambda$4134/71111758.accept(Unknown Source) ~[?:?] at v.a(SourceFile:401) ~[1.16.1.jar:?] at aoq.a(SourceFile:467) ~[1.16.1.jar:?] at aoq.b(SourceFile:530) [1.16.1.jar:?] at aoq.a(SourceFile:511) [1.16.1.jar:?] at chv.a(SourceFile:378) [1.16.1.jar:?] at chv.b(SourceFile:138) [1.16.1.jar:?] at chv$$Lambda$4047/691052308.accept(Unknown Source) [1.16.1.jar:?] at chj.w(SourceFile:479) [1.16.1.jar:?] at yp.a(SourceFile:622) [1.16.1.jar:?] at yp$$Lambda$4110/1666711156.apply(Unknown Source) [1.16.1.jar:?] at com.mojang.datafixers.util.Either.lambda$mapLeft$0(Either.java:162) [datafixerupper-3.0.25.jar:?] at com.mojang.datafixers.util.Either$$Lambda$2972/865600325.apply(Unknown Source) [datafixerupper-3.0.25.jar:?] at com.mojang.datafixers.util.Either$Left.map(Either.java:38) [datafixerupper-3.0.25.jar:?] at com.mojang.datafixers.util.Either.mapLeft(Either.java:162) [datafixerupper-3.0.25.jar:?] at yp.a(SourceFile:611) [1.16.1.jar:?] at yp$$Lambda$4107/699047167.apply(Unknown Source) [1.16.1.jar:?] at java.util.concurrent.CompletableFuture.uniApply(CompletableFuture.java:602) [?:1.8.0_51] at java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:577) [?:1.8.0_51] at java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:442) [?:1.8.0_51] at yr.b(SourceFile:58) [1.16.1.jar:?] at yr$$Lambda$4035/267684891.run(Unknown Source) [1.16.1.jar:?] at amn.c(SourceFile:144) [1.16.1.jar:?] at zb$a.c(SourceFile:545) [1.16.1.jar:?] at amn.x(SourceFile:118) [1.16.1.jar:?] at zb$a.x(SourceFile:554) [1.16.1.jar:?] at zb.d(SourceFile:280) [1.16.1.jar:?] at net.minecraft.server.MinecraftServer.aZ(SourceFile:751) [1.16.1.jar:?] at net.minecraft.server.MinecraftServer.x(SourceFile:739) [1.16.1.jar:?] at amn.c(SourceFile:127) [1.16.1.jar:?] at net.minecraft.server.MinecraftServer.w(SourceFile:724) [1.16.1.jar:?] at net.minecraft.server.MinecraftServer.v(SourceFile:676) [1.16.1.jar:?] at net.minecraft.server.MinecraftServer.a(SourceFile:256) [1.16.1.jar:?] at net.minecraft.server.MinecraftServer$$Lambda$3892/509140991.run(Unknown Source) [1.16.1.jar:?] at java.lang.Thread.run(Thread.java:745) [?:1.8.0_51]Caused by: java.lang.NullPointerException at java.util.Objects.requireNonNull(Objects.java:203) ~[?:1.8.0_51] at java.util.Optional.<init>(Optional.java:96) ~[?:1.8.0_51] at java.util.Optional.of(Optional.java:108) ~[?:1.8.0_51] at com.mojang.datafixers.util.Either$Left.left(Either.java:54) ~[datafixerupper-3.0.25.jar:?] at com.mojang.serialization.DataResult$Instance.ap3(DataResult.java:334) ~[datafixerupper-3.0.25.jar:?] at com.mojang.datafixers.Products$P3.apply(Products.java:176) ~[datafixerupper-3.0.25.jar:?] at com.mojang.datafixers.Products$P3.apply(Products.java:172) ~[datafixerupper-3.0.25.jar:?] at awl$b.a(SourceFile:75) ~[1.16.1.jar:?] at awl$$Lambda$4835/1477390246.apply(Unknown Source) ~[?:?] at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) ~[?:1.8.0_51] at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) ~[?:1.8.0_51] at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) ~[?:1.8.0_51] at java.util.Iterator.forEachRemaining(Iterator.java:116) ~[?:1.8.0_51] at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801) ~[?:1.8.0_51] at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:512) ~[?:1.8.0_51] at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:502) ~[?:1.8.0_51] at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151) ~[?:1.8.0_51] at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174) ~[?:1.8.0_51] at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[?:1.8.0_51] at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:418) ~[?:1.8.0_51] at awl.a(SourceFile:254) ~[1.16.1.jar:?] at bdp.a(SourceFile:527) ~[1.16.1.jar:?] at aom.f(SourceFile:1636) ~[1.16.1.jar:?] ... 36 more