EMR instance types are invalid with the same weight for different types
### Description

In all the EMR instance types properties, weights for the different instance types are set in-line with the instance types.

A validation predicate has been added for those properties which ensures that duplicate instance types are not set, but it includes the weights in the duplication test. This means that you can't set the same weight for more than one instance type.

### Steps to reproduce

1. Open the admin client with EmrBulkImportStack deployed
2. Update table property `sleeper.table.bulk.import.emr.master.x86.instance.types` to `m5.xlarge,2,m6i.xlarge,2`
3. See the property change fails to validate

### Expected behaviour

We should be able to set the same weight for multiple instance types on any instance types property.
diff --git a/java/configuration/src/main/java/sleeper/configuration/properties/validation/EmrInstanceTypeConfig.java b/java/configuration/src/main/java/sleeper/configuration/properties/validation/EmrInstanceTypeConfig.java
index 73c852553..9d5f312f5 100644
--- a/java/configuration/src/main/java/sleeper/configuration/properties/validation/EmrInstanceTypeConfig.java
+++ b/java/configuration/src/main/java/sleeper/configuration/properties/validation/EmrInstanceTypeConfig.java
@@ -75,6 +75,9 @@ public class EmrInstanceTypeConfig {
     }
 
     public static boolean isValidInstanceTypes(String value) {
+        if (value == null) {
+            return false;
+        }
         try {
             List<String> instanceTypes = readInstanceTypesProperty(readList(value), X86_64)
                     .map(EmrInstanceTypeConfig::getInstanceType)
diff --git a/java/configuration/src/test/java/sleeper/configuration/properties/validation/EmrInstanceTypeConfigTest.java b/java/configuration/src/test/java/sleeper/configuration/properties/validation/EmrInstanceTypeConfigTest.java
index 6231d6fa0..d1f14d7da 100644
--- a/java/configuration/src/test/java/sleeper/configuration/properties/validation/EmrInstanceTypeConfigTest.java
+++ b/java/configuration/src/test/java/sleeper/configuration/properties/validation/EmrInstanceTypeConfigTest.java
@@ -209,6 +209,12 @@ public class EmrInstanceTypeConfigTest {
             assertThat(EmrInstanceTypeConfig.isValidInstanceTypes("1,type-a"))
                     .isFalse();
         }
+
+        @Test
+        void shouldFailValidationWhenInstanceTypesPropertyIsNull() {
+            assertThat(EmrInstanceTypeConfig.isValidInstanceTypes(null))
+                    .isFalse();
+        }
     }
 
     public static Stream<EmrInstanceTypeConfig> readInstanceTypesProperty(List<String> instanceTypeEntries) {
['java/configuration/src/main/java/sleeper/configuration/properties/validation/EmrInstanceTypeConfig.java', 'java/configuration/src/test/java/sleeper/configuration/properties/validation/EmrInstanceTypeConfigTest.java']