Don't throw error on invalid data in CraftMetaItem.

src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaItem.java

@@ -384,22 +384,34 @@ class CraftMetaItem implements ItemMeta, Damageable, Repairable {
                 continue;
             }
             net.minecraft.server.AttributeModifier nmsModifier = GenericAttributes.a(entry);
-            Preconditions.checkNotNull(nmsModifier, "Could not create AttributeModifier. %s", entry.toString());
+            if (nmsModifier == null) {
+                continue;
+            }
 
             AttributeModifier attribMod = CraftAttributeInstance.convert(nmsModifier);
 
             String attributeName = entry.getString(ATTRIBUTES_IDENTIFIER.NBT);
-            Preconditions.checkArgument(!Strings.isNullOrEmpty(attributeName), "Missing Attribute for AttributeModifier. %s", entry.toString());
+            if (attributeName == null || attributeName.isEmpty()) {
+                continue;
+            }
 
             Attribute attribute = CraftAttributeMap.fromMinecraft(attributeName);
-            Preconditions.checkNotNull(attribute, "Could not convert to Bukkit Attribute. %s", attributeName);
+            if (attribute == null) {
+                continue;
+            }
 
             if (entry.hasKeyOfType(ATTRIBUTES_SLOT.NBT, CraftMagicNumbers.NBT.TAG_STRING)) {
                 String slotName = entry.getString(ATTRIBUTES_SLOT.NBT);
-                Preconditions.checkArgument(!Strings.isNullOrEmpty(slotName), "Missing Slot when Slot is specified. %s", entry.toString());
+                if (slotName == null || slotName.isEmpty()) {
+                    modifiers.put(attribute, attribMod);
+                    continue;
+                }
 
                 EquipmentSlot slot = CraftEquipmentSlot.getSlot(EnumItemSlot.a(slotName.toLowerCase(Locale.ROOT))); // PAIL rename fromName
-                Preconditions.checkNotNull(slot, "No Slot found when Slot was specified. %s", entry.toString());
+                if (slot == null) {
+                    modifiers.put(attribute, attribMod);
+                    continue;
+                }
 
                 attribMod = new AttributeModifier(attribMod.getUniqueId(), attribMod.getName(), attribMod.getAmount(), attribMod.getOperation(), slot);
             }
@@ -609,10 +621,14 @@ class CraftMetaItem implements ItemMeta, Damageable, Repairable {
             }
             net.minecraft.server.AttributeModifier nmsModifier = CraftAttributeInstance.convert(entry.getValue());
             NBTTagCompound sub = GenericAttributes.a(nmsModifier);
-            Preconditions.checkState(!sub.isEmpty(), "Could not convert AttributeModifier. It was supplied in an invalid format. The following was supplied: %s", sub.toString());
+            if (sub.isEmpty()) {
+                continue;
+            }
 
             String name = CraftAttributeMap.toMinecraft(entry.getKey());
-            Preconditions.checkArgument(!Strings.isNullOrEmpty(name), "Could not convert to Bukkit Attribute. %s", entry.getKey().name());
+            if (name == null || name.isEmpty()) {
+                continue;
+            }
 
             sub.setString(ATTRIBUTES_IDENTIFIER.NBT, name); // Attribute Name
             if (entry.getValue().getSlot() != null) {