diff --git a/sasjs-tests/src/testSuites/SpecialCases.ts b/sasjs-tests/src/testSuites/SpecialCases.ts
index 636c9c3..2bf9c88 100644
--- a/sasjs-tests/src/testSuites/SpecialCases.ts
+++ b/sasjs-tests/src/testSuites/SpecialCases.ts
@@ -80,7 +80,7 @@ const errorAndCsrfData: any = {
 }
 
 const testTable = 'sometable'
-const testTableWithNullVars: { [key: string]: any } = {
+export const testTableWithNullVars: { [key: string]: any } = {
   [testTable]: [
     { var1: 'string', var2: 232, nullvar: 'A' },
     { var1: 'string', var2: 232, nullvar: 'B' },
diff --git a/src/file/generateFileUploadForm.ts b/src/file/generateFileUploadForm.ts
index 5e2cdcc..e358c08 100644
--- a/src/file/generateFileUploadForm.ts
+++ b/src/file/generateFileUploadForm.ts
@@ -5,8 +5,11 @@ export const generateFileUploadForm = (
   data: any
 ): FormData => {
   for (const tableName in data) {
+    if (!Array.isArray(data[tableName])) continue
+
     const name = tableName
     const csv = convertToCSV(data[tableName])
+
     if (csv === 'ERROR: LARGE STRING LENGTH') {
       throw new Error(
         'The max length of a string value in SASjs is 32765 characters.'
diff --git a/src/file/spec/generateFileUploadForm.spec.ts b/src/file/spec/generateFileUploadForm.spec.ts
new file mode 100644
index 0000000..59fdc99
--- /dev/null
+++ b/src/file/spec/generateFileUploadForm.spec.ts
@@ -0,0 +1,55 @@
+import { generateFileUploadForm } from '../generateFileUploadForm'
+
+describe('generateFileUploadForm', () => {
+  beforeAll(() => {
+    function FormDataMock(this: any) {
+      this.append = () => {}
+    }
+
+    const BlobMock = jest.fn()
+
+    ;(global as any).FormData = FormDataMock
+    ;(global as any).Blob = BlobMock
+  })
+
+  it('should generate file upload form from data', () => {
+    const formData = new FormData()
+    const testTable = 'sometable'
+    const testTableWithNullVars: { [key: string]: any } = {
+      [testTable]: [
+        { var1: 'string', var2: 232, nullvar: 'A' },
+        { var1: 'string', var2: 232, nullvar: 'B' },
+        { var1: 'string', var2: 232, nullvar: '_' },
+        { var1: 'string', var2: 232, nullvar: 0 },
+        { var1: 'string', var2: 232, nullvar: 'z' },
+        { var1: 'string', var2: 232, nullvar: null }
+      ],
+      [`$${testTable}`]: { formats: { var1: '$char12.', nullvar: 'best.' } }
+    }
+    const tableName = Object.keys(testTableWithNullVars).filter((key: string) =>
+      Array.isArray(testTableWithNullVars[key])
+    )[0]
+
+    jest.spyOn(formData, 'append').mockImplementation(() => {})
+
+    generateFileUploadForm(formData, testTableWithNullVars)
+
+    expect(formData.append).toHaveBeenCalledOnce()
+    expect(formData.append).toHaveBeenCalledWith(
+      tableName,
+      {},
+      `${tableName}.csv`
+    )
+  })
+
+  it('should throw an error if too large string was provided', () => {
+    const formData = new FormData()
+    const data = { testTable: [{ var1: 'z'.repeat(32765 + 1) }] }
+
+    expect(() => generateFileUploadForm(formData, data)).toThrow(
+      new Error(
+        'The max length of a string value in SASjs is 32765 characters.'
+      )
+    )
+  })
+})
diff --git a/src/utils/convertToCsv.ts b/src/utils/convertToCsv.ts
index 9cc5565..73af3ba 100644
--- a/src/utils/convertToCsv.ts
+++ b/src/utils/convertToCsv.ts
@@ -3,7 +3,7 @@
  * @param data - the array of JSON objects to convert.
  */
 export const convertToCSV = (
-  data: any,
+  data: any[],
   sasFormats?: { formats: { [key: string]: string } }
 ) => {
   let formats = sasFormats?.formats
@@ -76,7 +76,7 @@ export const convertToCSV = (
               return byteSize
             }
           })
-          .sort((a: number, b: number) => b - a)[0]
+          .sort((a: any, b: any) => b - a)[0]
 
         if (longestValueForField && longestValueForField > 32765) {
           invalidString = true