diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java
index 3c58a95deeae..e0e409926dd1 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java
@@ -478,6 +478,11 @@ public Map<String, ModelsMap> postProcessAllModels(Map<String, ModelsMap> objs)
         for (Map.Entry<String, ModelsMap> entry : objs.entrySet()) {
             CodegenModel model = ModelUtils.getModelByName(entry.getKey(), objs);
 
+            if (model == null) {
+                LOGGER.warn("Null model found in postProcessAllModels: {}", entry.getKey());
+                continue;
+            }
+
             // add the model to the discriminator's mapping so templates have access to more than just the string to string mapping
             if (model.discriminator != null && model.discriminator.getMappedModels() != null) {
                 for (CodegenDiscriminator.MappedModel mappedModel : model.discriminator.getMappedModels()) {
@@ -5977,6 +5982,10 @@ Map<String, String> getAllAliases(Map<String, Schema> schemas) {
     }
 
     private static Boolean isAliasOfSimpleTypes(Schema schema) {
+        if (schema == null) {
+            return false;
+        }
+
         return (!ModelUtils.isObjectSchema(schema)
                 && !ModelUtils.isArraySchema(schema)
                 && !ModelUtils.isMapSchema(schema)
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultGenerator.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultGenerator.java
index 471b0364fe0c..be8aeeae5472 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultGenerator.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultGenerator.java
@@ -1334,8 +1334,10 @@ private ModelsMap processModels(CodegenConfig config, Map<String, Schema> defini
         for (Map.Entry<String, Schema> definitionsEntry : definitions.entrySet()) {
             String key = definitionsEntry.getKey();
             Schema schema = definitionsEntry.getValue();
-            if (schema == null)
-                throw new RuntimeException("schema cannot be null in processModels");
+            if (schema == null) {
+                LOGGER.warn("Schema {} cannot be null in processModels", key);
+                continue;
+            }
             CodegenModel cm = config.fromModel(key, schema);
             ModelMap mo = new ModelMap();
             mo.setModel(cm);
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/InlineModelResolver.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/InlineModelResolver.java
index e395be243324..20ce9f3ad403 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/InlineModelResolver.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/InlineModelResolver.java
@@ -286,6 +286,11 @@ private void gatherInlineModels(Schema schema, String modelPrefix) {
             if (props != null) {
                 for (String propName : props.keySet()) {
                     Schema prop = props.get(propName);
+
+                    if (prop == null) {
+                        continue;
+                    }
+
                     String schemaName = resolveModelName(prop.getTitle(), modelPrefix + "_" + propName);
                     // Recurse to create $refs for inner models
                     gatherInlineModels(prop, schemaName);
@@ -308,13 +313,15 @@ private void gatherInlineModels(Schema schema, String modelPrefix) {
             if (schema.getAdditionalProperties() != null) {
                 if (schema.getAdditionalProperties() instanceof Schema) {
                     Schema inner = (Schema) schema.getAdditionalProperties();
-                    String schemaName = resolveModelName(schema.getTitle(), modelPrefix + this.inlineSchemaOptions.get("MAP_ITEM_SUFFIX"));
-                    // Recurse to create $refs for inner models
-                    gatherInlineModels(inner, schemaName);
-                    if (isModelNeeded(inner)) {
-                        // If this schema should be split into its own model, do so
-                        Schema refSchema = this.makeSchemaInComponents(schemaName, inner);
-                        schema.setAdditionalProperties(refSchema);
+                    if (inner != null) {
+                        String schemaName = resolveModelName(schema.getTitle(), modelPrefix + this.inlineSchemaOptions.get("MAP_ITEM_SUFFIX"));
+                        // Recurse to create $refs for inner models
+                        gatherInlineModels(inner, schemaName);
+                        if (isModelNeeded(inner)) {
+                            // If this schema should be split into its own model, do so
+                            Schema refSchema = this.makeSchemaInComponents(schemaName, inner);
+                            schema.setAdditionalProperties(refSchema);
+                        }
                     }
                 }
             }
@@ -334,10 +341,6 @@ private void gatherInlineModels(Schema schema, String modelPrefix) {
         if (schema instanceof ArraySchema) {
             ArraySchema array = (ArraySchema) schema;
             Schema items = array.getItems();
-            /*if (items.getTitle() != null) {
-                LOGGER.info("schema title {}", items);
-                throw new RuntimeException("getTitle for array item is not null");
-            }*/
             if (items == null) {
                 LOGGER.error("Illegal schema found with array type but no items," +
                         " items must be defined for array schemas:\n " + schema.toString());
@@ -360,6 +363,9 @@ private void gatherInlineModels(Schema schema, String modelPrefix) {
                 List<Schema> newAllOf = new ArrayList<Schema>();
                 boolean atLeastOneModel = false;
                 for (Object inner : schema.getAllOf()) {
+                    if (inner == null) {
+                        continue;
+                    }
                     String schemaName = resolveModelName(((Schema) inner).getTitle(), modelPrefix + "_allOf");
                     // Recurse to create $refs for inner models
                     gatherInlineModels((Schema) inner, schemaName);
@@ -392,6 +398,9 @@ private void gatherInlineModels(Schema schema, String modelPrefix) {
             if (schema.getAnyOf() != null) {
                 List<Schema> newAnyOf = new ArrayList<Schema>();
                 for (Object inner : schema.getAnyOf()) {
+                    if (inner == null) {
+                        continue;
+                    }
                     String schemaName = resolveModelName(((Schema) inner).getTitle(), modelPrefix + "_anyOf");
                     // Recurse to create $refs for inner models
                     gatherInlineModels((Schema) inner, schemaName);
@@ -407,6 +416,9 @@ private void gatherInlineModels(Schema schema, String modelPrefix) {
             if (schema.getOneOf() != null) {
                 List<Schema> newOneOf = new ArrayList<Schema>();
                 for (Object inner : schema.getOneOf()) {
+                    if (inner == null) {
+                        continue;
+                    }
                     String schemaName = resolveModelName(((Schema) inner).getTitle(), modelPrefix + "_oneOf");
                     // Recurse to create $refs for inner models
                     gatherInlineModels((Schema) inner, schemaName);
@@ -423,12 +435,14 @@ private void gatherInlineModels(Schema schema, String modelPrefix) {
         // Check not schema
         if (schema.getNot() != null) {
             Schema not = schema.getNot();
-            String schemaName = resolveModelName(schema.getTitle(), modelPrefix + "_not");
-            // Recurse to create $refs for inner models
-            gatherInlineModels(not, schemaName);
-            if (isModelNeeded(not)) {
-                Schema refSchema = this.makeSchemaInComponents(schemaName, not);
-                schema.setNot(refSchema);
+            if (not != null) {
+                String schemaName = resolveModelName(schema.getTitle(), modelPrefix + "_not");
+                // Recurse to create $refs for inner models
+                gatherInlineModels(not, schemaName);
+                if (isModelNeeded(not)) {
+                    Schema refSchema = this.makeSchemaInComponents(schemaName, not);
+                    schema.setNot(refSchema);
+                }
             }
         }
     }
@@ -629,6 +643,9 @@ private void flattenComponents() {
         List<String> modelNames = new ArrayList<String>(models.keySet());
         for (String modelName : modelNames) {
             Schema model = models.get(modelName);
+            if (model == null) {
+                continue;
+            }
             if (ModelUtils.isAnyOf(model)) { // contains anyOf only
                 gatherInlineModels(model, modelName);
             } else if (ModelUtils.isOneOf(model)) { // contains oneOf only
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/ModelUtils.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/ModelUtils.java
index e3edb79ff39b..838df6ce5e09 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/ModelUtils.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/ModelUtils.java
@@ -438,6 +438,10 @@ public static boolean isTypeObjectSchema(Schema schema) {
      * @return true if the specified schema is an Object schema.
      */
     public static boolean isObjectSchema(Schema schema) {
+        if (schema == null) {
+            return false;
+        }
+
         return (schema instanceof ObjectSchema) ||
                 // must not be a map
                 (SchemaTypeUtil.OBJECT_TYPE.equals(schema.getType()) && !(schema instanceof MapSchema)) ||
@@ -549,6 +553,10 @@ public static boolean isComplexComposedSchema(Schema schema) {
      * @return true if the specified schema is a Map schema.
      */
     public static boolean isMapSchema(Schema schema) {
+        if (schema == null) {
+            return false;
+        }
+
         // additionalProperties explicitly set to false
         if (schema.getAdditionalProperties() instanceof Boolean && Boolean.FALSE.equals(schema.getAdditionalProperties())) {
             return false;
@@ -1858,6 +1866,10 @@ public static boolean isAllOfWithProperties(Schema schema) {
      * @return true if the schema contains oneOf but no properties/allOf/anyOf defined.
      */
     public static boolean isOneOf(Schema schema) {
+        if (schema == null) {
+            return false;
+        }
+
         if (hasOneOf(schema) && (schema.getProperties() == null || schema.getProperties().isEmpty()) &&
                 (schema.getAllOf() == null || schema.getAllOf().isEmpty()) &&
                 (schema.getAnyOf() == null || schema.getAnyOf().isEmpty())) {
@@ -1875,7 +1887,7 @@ public static boolean isOneOf(Schema schema) {
      * @return true if allOf is not empty
      */
     public static boolean hasOneOf(Schema schema) {
-        if (schema.getOneOf() != null && !schema.getOneOf().isEmpty()) {
+        if (schema != null && schema.getOneOf() != null && !schema.getOneOf().isEmpty()) {
             return true;
         }
 
@@ -1890,6 +1902,10 @@ public static boolean hasOneOf(Schema schema) {
      * @return true if the schema contains oneOf but no properties/allOf/anyOf defined.
      */
     public static boolean isAnyOf(Schema schema) {
+        if (schema == null) {
+            return false;
+        }
+
         if (hasAnyOf(schema) && (schema.getProperties() == null || schema.getProperties().isEmpty()) &&
                 (schema.getAllOf() == null || schema.getAllOf().isEmpty()) &&
                 (schema.getOneOf() == null || schema.getOneOf().isEmpty())) {
@@ -1907,7 +1923,7 @@ public static boolean isAnyOf(Schema schema) {
      * @return true if anyOf is not empty
      */
     public static boolean hasAnyOf(Schema schema) {
-        if (schema.getAnyOf() != null && !schema.getAnyOf().isEmpty()) {
+        if (schema != null && schema.getAnyOf() != null && !schema.getAnyOf().isEmpty()) {
             return true;
         }