Histogram: filter nulls, bucket-adaptive xAxis decimals (#51773) (#51822)

(cherry picked from commit 173636aa61)

Co-authored-by: Leon Sorokin <leeoniya@gmail.com>

packages/grafana-data/src/transformations/transformers/histogram.ts

@@ -165,6 +165,8 @@ export function buildHistogram(frames: DataFrame[], options?: HistogramTransform
       }
     }
 
+    allValues = allValues.filter((v) => v != null);
+
     allValues.sort((a, b) => a - b);
 
     let smallestDelta = Infinity;
@@ -202,6 +204,9 @@ export function buildHistogram(frames: DataFrame[], options?: HistogramTransform
 
   const getBucket = (v: number) => incrRoundDn(v - bucketOffset, bucketSize!) + bucketOffset;
 
+  // guess number of decimals
+  let bucketDecimals = (('' + bucketSize).match(/\.\d+$/) ?? ['.'])[0].length - 1;
+
   let histograms: AlignedData[] = [];
   let counts: Field[] = [];
   let config: FieldConfig | undefined = undefined;
@@ -249,7 +254,13 @@ export function buildHistogram(frames: DataFrame[], options?: HistogramTransform
     values: new ArrayVector(joinedHists[0]),
     type: FieldType.number,
     state: undefined,
-    config: config ?? {},
+    config:
+      bucketDecimals === 0
+        ? config ?? {}
+        : {
+            ...config,
+            decimals: bucketDecimals,
+          },
   };
   const bucketMax = {
     ...bucketMin,