Fix footstep particle causing null kick (#4287)

api/src/main/java/com/viaversion/viaversion/api/data/FullMappingsBase.java

@@ -95,7 +95,7 @@ public class FullMappingsBase implements FullMappings {
     }
 
     @Override
-    public String mappedIdentifier(final int mappedId) {
+    public @Nullable String mappedIdentifier(final int mappedId) {
         if (mappedId < 0 || mappedId >= mappedIdToString.length) {
             return null;
         }

common/src/main/java/com/viaversion/viaversion/protocols/v1_21to1_21_2/rewriter/ParticleRewriter1_21_2.java

@@ -45,10 +45,10 @@ public final class ParticleRewriter1_21_2 extends ParticleRewriter<ClientboundPa
         super.rewriteParticle(connection, particle);
         
         final String identifier = protocol.getMappingData().getParticleMappings().mappedIdentifier(particle.id());
-        if (identifier.equals("minecraft:dust_color_transition")) {
+        if ("minecraft:dust_color_transition".equals(identifier)) {
             floatsToARGB(particle, 0);
             floatsToARGB(particle, 1);
-        } else if (identifier.equals("minecraft:dust")) {
+        } else if ("minecraft:dust".equals(identifier)) {
             floatsToARGB(particle, 0);
         }
     }